cab clearance

Had my 2013 Hawk on a 2013 F150 and just got my new 2018 F250. What I thought would be a 5" clearance from the top of the truck cab to the bottom of Hawk overhang is actually 2" with this new truck. FWC is saying, I should really have a 3"-6" clearance to be safe. I wonder if anyone has had...