The feathers aren't being slowed down by drag as much as the vanes are while going through the bisquit. That might be one reason they're shooting higher, but I doubt it.

I think the probable reason might be your nockset is off just a smidge and the vanes are being deflected downward slightly as they go through the rest. Might try tweaking your nock height to see if you can get the vanes to group with the feathers. At 20 yards, they really should group together.