What is the minimum clearance I need between the truck cab and camper overhang?

I built a 1" insulated lift for my TC thatworked fine for several years but it only provided 1/4" cab clearance. I recently built a 1-1/2" insulated lift which gives 3/4" lift. It has never caused an issue. I may have posted a spammy video here about it last year. The new lift also helps center and keep straight in the bed, how the TC sits.