Like Ekka said... The VT crew is here....
aaaaaaaah young wallaby's gear came through ay....
Nice gear mate. Nice setup too. Bit bulky for now but hey, you are doin' it safe. The reason why this could be difficult to advance is because the sheaves of that pullet touch each other when in closed position. You need to check if the climbing line doesn't touch the sheaves when it's advancing. If it does, that could cause some additional friction.Best pulley for a self advancing knot is the petzl fixe.It has fixed sheaves but the are some 1.5 cm's apart at the tie-in point so they don't touch the rope when advancing.
I hope this helps out....