Hi Tom, I could probably do more to help. I have the test equipment, just limited time and still using 13As exclusively.
As discussed last time, you should not need more than 1 uF for local decoupling (the C spanning pins 4 and 8). So 10-20 uF in the C1 spot and an additional 1 uF directly across pins 4-8 should do the trick. It really is not normal for the 13A to work as well as it does without proper decoupling.
I just recently set up a ‘test-bench’ with an A6 driver in the open. The di/dt spiking/ringing on the FET drain pin is impressive. A second improvement you can try is to add 100-200 ohm resistance between the MCU output pin and the FET gate. This will slow the FET switching and reduce the inductive ringing. Depending on the driver PCB layout you will probably have to cut and scrape a track to fit this resistor.