Also depends on what formation you're playing.

For example:

If you're playing a 4-5-1V and passing down the flanks, your MC players will not do much for your team other than defend, and they'll usually get fairly average form (at least my scout MCs do)

But my AMR/AMLs consistently get good form, as the team revolves around them.

Perhaps tell us what position they play and your formations, arrows?