Hmm no limitation, wonder why I was not able to do it early on.
Probably because of the little mouse touchyness I described I'd fathom to guess.
Need to be pretty much dead center or it rejects the object your trying to put in the slot.
If all else fails run
after you pick off one guy. They'll only follow you so far before they hit an invisible wall they can't go past. Then work in and pick off another before the melee guys get to you and go back to safe zone to heal or recharge. I've used that trick/some might consider cheat plenty.
