If it were me, in the interest of getting it done on time, I'd let the builder do whatever he normally does and change it later if you don't like it. Your tires are outside the tub so height doesn't matter for tire clearance. I know you're shooting for the max height of 6', but if it's a little taller than that it's not the end of the world, and once you have it in your hands you can decide if it needs to be changed.