So I’ve always been under the impression that positioning for an offensive (attacking) team isn’t necessary, this is said whilst ignoring heroes that buff adjacent heroes.
As the computer presumably attacks randomly (yet still hits my Proteus 5 times in a row), I don’t feel like placing the appropriate heroes in the tank, flank and wing positions improve/reduce your success rate.
It is better to place your two most key heroes in the corners (unless there is Jabberwock on the other team). This is because heroes who hit 3 (GM, Hel, Drake) will be less likely to attack them (and they won’t be able to hit two of your most important heroes at the same time).