I don't think the Eisenkern sets currently available from Wargames Atlantic are very much taller than the Cannon Fodder - I've mixed-and-matched pieces between these sets with no trouble at all, and the figures look fine mixed together.
As @John Wilson said, the Eisenkern kits are great for "light" Star Wars Stormtrooper style sci-fi combat armor, at least, and could probably pass for lighter Iron Man style power armor as well.
Iron Man: Sure, the helmet and other details are different, but I think you get what I mean: this power armor isn't very bulky at all....
Bubblegum Crisis: Japan was mad about the power armor trope, too. The Eisenkern figures would work fine for this sort of light, form-fitted power armor (high-heeled iron boots and swords not included.)
Robocop: Technically a cyborg, but he falls pretty closely into the power armor trope as well, and Eisenkern figures could probably substitute for this sort of character concept as well.
I think the Iron Core Valkir look like they'd definitely work in my book as heavier power armor.
Valkir: A bit more like the heavy power armor I imagine first. They remind me of 40K and Starcraft style space marines, which I think would count as well, really.
G.I.Joe "S.N.A.K.E." Combat Armor: A bit stiff and boxy, but quite a bit more like heavy power armor as I imagine it, and it definitely fits the heavy power armor mold in my book.
Reaper Miniatures IMEF Bulldog: Another heavy power armor concept that hits pretty close to what I imagine. The "head" of the vehicle is a hatch that can be posed closed, or (as in this illustration) open to reveal the pilot's head. It should make for a pretty substantial power armor suit, more so than might be practical or desirable for a hard plastic kit, as you're really approaching something more like a vehicle, or something that might be suited to a single figure per sprue, including arm options and other optional bits.
Shogun Warriors: At the more extreme end of the Japanese power armor craze of the '80s, you started crossing over into giant "robot" territory - all the better to battle giant kaiju monsters with! Prepare your kung-fu moves, Grab your Garmin, and save the day! (Plucky but psychologically damaged Japanese school-kid pilots not included.)
When I was a youngster back in the '80s, there used to be Japanese hard plastic model kits for "Mobile Suit Gundam" figures in that anime style available in your friendly local model-building shops, but I've never seen one in person to guess at how well they'd work for 28mm gaming, and I don't know if they're still around. They were apparently 1/100 scale, but might still look impressive enough alongside 28mm figures to work, if you can still find them.
Mobile Suit Gundam: Most figures looked more like "Shogun Warriors" or Neon Genesis "EVA" suits, but this model is very close to what I had always pictured the MI power armor from Starship Troopers looking like, but again, your mileage may vary. If there's a low-cost stash of these still out there, and they look credible alongside 28mm minis, I'd grab and build a couple, then try to find some excuse to use them!
Star Wars AT-ST: Also on the more extreme end of the power suit spectrum would be the "Battle Mech" concepts like this (relatively) small one. I'm pretty sure a couple companies, including GW, make this sort of vehicle kit in 28mm scale, and these mechs look great to me on a sci-fi battlefield, even if they are a bit impractical for 28mm scale wargaming! (I really don't feel like vehicle combat is a good subject per se for 28mm miniature wargaming - these larger vehicles might work best on the tabletop as scenery or objectives, rather than mobile vehicles, due to the limited space on the typical game table....)
Reaper Miniatures Blackstar Corsair: Your mileage may vary, but for me, this is a heavy power armor concept that pretty much hits a "sweet spot" for me between the extremes of the lighter Eisenkern figures on one hand, and the IMEF Bulldog and giant robot stuff above, especially on a budget, and it's what I'll probably go to first for most general-purpose tabletop power armor purposes, unless WGA does something even more perfect for me.
The Valkir look like they'll be a great power-armor set as well, and I might grab a box of those when they're available, since the mix really well with the versatile Eisenkern figures I'm already using for various sci-fi gaming purposes.
A blurry early picture of one of my Eisenkern kitbashes - a couple of the figures in the back have been mixed with Cannon Fodder bodies; foreshortening from the camera perspective aside, most of these figures are pretty much the same height. Everyone seems comfortable holding AK type weapons. The running figure in the front is a female Eisenkern figure. A Blackstar Corsair power armor suit is included as well, which might help with a size comparison: a typical 28mm sci-fi figure is just about shoulder-height to the Corsair, making it about 7 feet tall, assuming ~6-foot tall Cannon Fodder and Eisenkerns: tall and bulky enough to stand out on a gaming table, while still being compact enough to plausibly squeeze/duck through residential door frames, walk through starship or building corridors, and into/out of roomy APCs and dropships.
Anyway, the Valkir look like they'll make fine medium-light power armor, and Reaper has an option or two for something a little heavier, but I think a Wargames Atlantic power armor set would be great, and would absolutely make a fine Death Fields Japanese faction, given the long power armor tradition in Japanese sci-fi!
"Yes, we will use the latest technical devices. Already now they are being stationed, for example, in the southern parts of our country."
- Vladimir Putin, 2006, when asked whether Russia planned to use gigantic, humanoid war robots.
"These are unmanned aerial vehicles. And maybe the time will come for gigantic robots. However, so far we have put our main hope on people, namely border guards." - Vladimir Putin, 2006, clarifying his statement.
"I view such mysterious forces with suspicion... there is something more behind such questions, and I advise people who take this seriously to read a holy book." - Vladimir Putin, 2006, on a follow-up question about whether the stars were right for Great Cthulhu to rise from its watery slumber and walk free upon the earth. (Read a holy book, and, no doubt, prepare the gigantic war robots and plucky Japanese school-kid pilots!)