I balance my tail and head the same, as an assembly.

First, if they're woodies, balance the blades to themselves, taking in to consideration lead and lag and tip to root. Like you've done, just balance the tail blades by sanding the tips.

Now, spin the thing up with the blades a little loose. Let it come to a stop on it's own and tighten the blade bolts a little making sure the blades don't move. Spin it up again, stop and tighten a little more. Do again 'till blades are snug.

Now remove the tail hub/blades and balance as an assembly on a center or high-point balancer.

Remove the head/blades/swash/main shaft assembly and balance on a high-point.

This method will identify bent main shafts and spindles too.

Kirk