OK, I started with 5-0-0-2W-3 this time and it WAS illegal. Not sure why it wasn't showing that way in previous tests.
I Immediately switched to 5-0-2W-0-3 and left that until the 29th minute, long enough to confirm it was illegal. Then i moved the MR and ML to AMC slots and played until halftime. Possession remained 20/80 throughout.
Sorry, only 1 screen cap, I screwed the others up up somehow.
Second half, trailing 3-2 I moved everyone forward, even tried to move the keeper into attack but it wasn't allowed! Pulled out a draw - experiment or not, clinched or not, I had to at least try for the league win LOL.
Anyway, I'll play a friendly later on, but after all this i think Potemy's 3 midfielders (AM*, M* or DM*) is correct. Now need to confirm if location of the 3 matters.