Range checks must be line of site. That means nothing between you and the airplane. Also an engine off range checks is only half a range check, the next step is a range check with the running an momentarily throttled up to full power working with an assistant of course. This is even doubly important for the FM,AM systems.
The figures you got are OK but back when I used 72Mhz I preferred to see antenna down at least 100 feet. Some brands struggled with that though.
John