Don't quote me but:
I think you are confusing ML and MLOA (my definitions). ML is the three or four days you are doing each month on your days off. You do not get B fund contributions for these. You get B fund contributions when you leave the company for greater than a period of 30 days, like you would for an activation. You no longer bid, you don't accrue vacation, lose CASS privileges (I think), but you do get B fund contributions. I believe they are based on your 12 month trailing average BLG (yours personally, not the fleets) and paid at your last pay rate, not some planned upgrade rate. The contribution is made in lump sum, when you return to the company following MLOA.