I just received my game today and wanted to put to rest once and for all the question on Basing these guys.
I used the Brother Claudio due to his wide stance.
I put him on top of a small square, small round and medium round bases.
I also have shown him on the medium base on a corridor tile.
He fits just fine.
Does the base extend past the drawn on floor grating? a little,but so what.
My Terminators will be going on proper Termie sized bases.
(Edit it was pointed out to me that 5 Termie bases would not fit on the peice.)
So I guess it is magnetized/small base.