The B screw shouldn't need to be super optimized just for the RD to drop the chain into the smallest cog. Assuming the hanger is now close enough to aligned, that really only leaves friction issues. This could be isolated by disconnecting the RD from the cable completely. Shift it into the 13 by moving the parallelogram with manually, ie with your hand, and then let it go. If it drops right into the 12, then you have a hang up along your cable somewhere. If it still won't drop in, there's not much left except a still bent hanger, stiff pivots, or a weak spring in the derailleur. Maybe a tweaked jockey cage. I'd make sure your cable is moving smoothly first.

Personally I advocate plenty of grease. No cable has not moved because it had too much grease. However, if you are using high tech prelubed cables, along with the correct matching housing, you don't need too. OT but this was a big religious debate when lined housing first came out.

Also make sure any linings are properly opened up with an awl, and housing ends are ground smooth.