massive reconfiguration time again.

I'm not expert but the timing shows up on the ground strap.
color starts at the bottom of the bend of your ground strap. At Least the best i can see from that picture angle.
Do you have a o2 to watch your air fuel ratio. Is it possible that it's getting to lean at cruising speed.
If you add timing the ground strap burn mark get longer, if you add fuel the same burn mark gets shorter. and less would make it longer.
In my opinion the white is only for reading detonation.
Did you go to a colder spark plug???? the length of the ground burn mark will also change with a colder plug. pulls more heat out of the plug, aka ground strap doesn't get as hot.

I'm just a amiture at plug reading so open to be educated.