Trad - bear in mind, lowering the fender should also change the radius of the fender. It's based off a concentric arc.
Also, the brace "legs" may have a slight angle to them which needs to be accounted for if you section there (front to back, parallel to the ground) in order to drop the fender.
Without doing the calculations, if think you might need to "pie cut" the brace along the leg, to tuck the fender mounting holes back into alignment, then remove some length from the lower edge of the fender, from the brace leg.
Does any of that make sense?
Another member modified his brace in a similar way, but made a great deal of small kerf cuts to reshape and resize the brace.that seems a lot more work to me.