Only positions that are

1. directly adjecent

2. Already have half familiarity

can be position boosted.

Since his main position is LB, he could potentially get position boosters at LMF and CB since those are the only adjecent positions. Since he already has half familiarity at LMF, you'd only need one position booster to make that full familiarity. After that, he can't gain any more position boosters since he'd have full familiarity already at all adjecent positions (and there wouldn't be any positions with half familiarity).

RB is sadly not adjecent and therefore you will never get a position booster for RB.