>>6712967The reason for this is that you're meant to rely on a headmaster's own neck joint for the super mode head (also WOW I did not notice how bad Convobat's head lit up under flash, here).
It's worth a mention that I think this actually looks pretty neat on it's own without the helmet, and would work nice as a replacement neck joint for PMOP/Ginrai, but it wouldn't fit in the stock cab without modification (it does fit in the mushroom peg hole, but stuff around it gets in the way).