The car should go where the rear is pointed--the front has to be fixed to lead- the wheelbase is pretty much irrelavent if only a few inches
Garlits rear engine dragster had about 8 inches of wb stagger and it went straigt
NHRA then limited it to 2 inches and they all go sraight

Your front end is probably staggered and the guy has aligned the front wheels parallel and square to each other instead of to the driving wheels

Go somewhere else---your guy isn't getting it done and you aren't going to change him or his ways