guess i answered my own question after searching the firmware changelog. Anyways, maybe it will help the next guy
# config.ign_dwellmap configurable MAP-based dwell scaleup (VBATT based is automatic)
* 00 no dwell extension at all (neither VBATT nor MAP based): ign_dwell14 is used
* 01 only VBATT based dwell extension (max *2, when VBATT <= 7V)
* values 02..FF : VBATT based extension is automatic. Slope of MAP-based dwell-extension is configured with this variable. MAP-based extension is max *1.4 (+40%), while total scaleup (vbattmultiplier * mapmultiplier) is max *2
o dwell is extended by (map - 70kPa) * ign_dwellmap/4096 but no more than +0.4 (40% extension that is *1.4). Examples:
o ign_dwellmap=0A (decimal 10) max dwell-extension +40% reached at 234 kPa because (234 kPa - 70 kPa) * 10 /4096 = 0.4
o ign_dwellmap=14 (decimal 20) max dwell-extension +40% reached at 152 kPa because (152 kPa - 70 kPa) * 20 /4096 = 0.4
o higher value means higher slope (so max dwell extension reached earlier). Take care not to overload the ignition output or the coil (use lower ign_dwell14 so you only get extended dwell when really necessary).
Currently my ign_dwellmap=0E (decimal 14).
I'll probably change it to at least 10, or possibly reduce my standard dwell time. I scoped a stock BMW, and its dwell time is 3.2ms. Which seems a little long to me, but thought it would be good under boost. guess vems already has that taken care of for me!