As usual, RapidRobert is on the money with his expertise.

Yes, your dwell decreased because of the increase in the gap. Dual point distributors came into being as a way to get more dwell (coil saturation) without doing it via a small point gap. Often, the "make" set can get by with a slightly closer gap and not show abnormal deterioration. If you see symptoms of weaker spark at the high RPMs, consider closing up the gap on the "make" set to get some dwell back (while leaving the gap on the "break" set alone).