Take some scrap aluminium. Bump that to at least 800-1000rpm, fill the hole with WD-40 or A9 and see if it'll bang it in 1 shot no pecking, use a good OSG spiral flute tap for AL. Then inspect the thread to see if its actually right, maybe something else is wrong with your code or whatever else. If it looks all good, then try it with your coolant, if it goes to hell, well I guess its your coolant.
Maybe also consider form tapping.
I go .70" deep in 304 stainless in one shot with 1/4-20's and cutting oil, 600rpm, rich coolant won't quite "cut it". AL likes a lot of lubricity too. Make sure the chips make it out of the hole and don't stick to the tap before it enters the next hole. When worried I call each hole as its own thing and M0, clean tap, fill hole, tap it, next. Yeah its a bit slower but nobody wins the race to making scrap parts either, 1000's oh holes would be a different story though.
I program in IPM for my rigid tapping, cad/cam thing, works fine, not sure what a Brother wants to eat for code though.
I too start about 1/2" away from the part.