I’ve had this happen to me twice. The first time I had only a 1/3 inch bed mat in the truck and I hit a deep whole that I didn’t see on the back side of a cattle guard. The cab over struck the truck roof and the shark fin antenna punched a whole in the cab over. A very expensive repair! So I put the 3/4 inch stall mat under the bed mat. Then on another trip, I hit a deep hole on a forest road that I again didn’t see (that dappled sunlight is pretty but makes irregularities in the road hard to see). This time the antenna only slightly cracked the fiberglass skin of the cab over. In both cases I was going less than 20 MPH on forest roads.
From now on when I plan to drive those typed of roads I will have 2x’s (laid flat) under 3/4 inch plywood plus the bed mat. That should give me just over 2.5 inches of additional distance between the cab and cab over. We’ll see how it works.