Permanent magnets can trick you into thinking, that 20kg of attraction force is easily achieved. Everyone seen electromagnetic locks, some can do almost 500kg of holding force! However, magnets from electromagnetic locks differ from rare-earth ones, since rare earth magnets can do the same with very long magnetic loops, gangsta!

Achieving something similar without superconductive magnets is quite tricky. So for almost a year I worked onto control circuit that can maintain EMF without converting it into heat very much. And even got some great results, however with current semiconductors it helps 50/50: very impressive overall, not enough for my application. So...

It's obvious for me now, but month ago it truly wasn't : )
There was something that can be done with magnetic "design":

There, poles of an electromagnet are pretty close to poles of a permanent magnet (or steel bar), with that in mind it's closer to electromagnetic locks, while by trying to align magnets, it still has somewhat nice operating range.

How gap affects force? I've made a simple setup with my desktop CNC to sorta map it:

As I use parts from an old disk drive as a linear rail for magnet, it had a very noticeable friction. Also, linkage between scales and a moving magnet wasn't perfect, as it tended to be springy...

But that was enough to get needed data:

As you can see, gap affects performance very much. I can make an educated guess that it would be full holding force with a gap shrinking to zero. That means that some tolerance in making artificial muscles, as it is for now, is needed to make them perform well

Hopefully, it shouldn't affect their semi-softness
P.S. Summer is over, uhh
P.P.S. Someone knows when JapanPost will resume shipping worldwide? I have ordered a pair of mugs half a year ago, they are still there, ahaha, it's really confusing