Hey Ian,

try setting B5156 to "0" and see what effect you have. B5156 is the "Maximum allowed spark retard amount due to knock, torque reduction etc." so it should help.

Along the same lines B5153 could also be adjusted to set the minimum spark timing as a separate control from B5156.

Finally, B5157 gives a final minimum timing MAP to set up. You could look at your logs for the exact RPM vs gm/Cyl points where you get the reductions and adjust this MAP to clip the minimum timing to a specific point.

Simon