I'm not worried about the drop; it's due to the load of everything in the system. "Jumping a reg" is a misnomer. If you want to set the output of the alternator to full, with NO regulation, you disconnect the white field wire from the reg, and jump it,(the wire, not the reg term) to the bat+.
And remember, even under the best conditions, these systems are RPM dependant.
I add that jumping is ONLY for test purposes, and I wouldn't even bother, given your results of (IMO) the only valid resistance reg test.