Determine Ride Height on a Frame Up Build?

[BBShark]

I would like to know how you determine the finished ride height before the car is finished for a car with a one of a kind suspension? I know that you have some flexibility with coilovers but I'm not sure how you account for tire "squish" when all of the weight (of the finished car) is on the tires. I thought this dimension might be negligible but I measured my daily driver and came up with 1 1/2 inches of difference on a 28 inch diameter tire (distance from ground to center of wheel = 12 1/2 inches). That is significant.

So, is there a fixed number you use or do the tire manufacturers give you this info or................?