Firstly, thank you for playing!
About the shield guys - they actually can surround you - it's just currently random whether or not they *will*. IIRC it also has to do with whether or not they can actually path to a spot within 5 meters (or something like that) of you. This is partly a level design issue, I acknowledge.
and as for the shields themselves... ugh... this is one of those things I've been meaning to work on - and have gotten a lot of comments about. But I'm not really sure how to fix it. Right now the way it works is that all enemies just use one capsule collider for damage, and the shield guys just take less damage from the front, and more from the back. So the idea is that the ideal strategy is to keep tabs on where they are, keep yourself from getting surrounded, and hit them from the back (phrasing).
I guess I could add a flat box/plane collider to the front of them that does the same thing, but then it wouldn't necessarily be able to match up with the way the shield on the sprite moves.
And there *is* a pain state animation where they sorta do what you're describing, it just appears that it doesn't show up enough/goes by too quickly for players to notice.