10.4 is very rich. 10.9 is rich, but not that far off. I like low 11s AFR for a non-charge cooled roots blower car like yours. With an intercooler, mid-high 11s are OK.
Also note that you are going to be richer still (generally by .5 AFR, but it depends on nozzle size and water/meth ratio) when the meth is flowing.
I'd take a good look at your fueling and make some changes. I don't like that your AFR fluctuates by .5 at WOT (that's way too much) and wonder if you have a mechanical fuel delivery issue (dirty filter, weak pump) or a tune issue (MAF not dialed in). Is it getting richer or leaner during a pull? Once you get AFR to not fluctuate so much I'd lean it out to the low 11 range.