One option to discuss with your DAR is the taking of many detailed pics of the area below the tank and behind the bulkhead. My DAR wanted to see a taxi /brake test, which meant that the tank had to be installed and the plane running. And, he wanted not to be there for many hours for eyeballing that stuff then waiting for the tank to be installed. The pics sufficed.
Vans should just split the rear bulkhead and eliminate this problem. Van's personal RV12 has the bulkhead split just like in the mods thread. It is a touchy issue but your DAR might be OK with a split bulkhead or depending on their familiarity with the 12 may have no idea it is not supposed to be like that, or even care. After all, it is YOU that has to sign the statement that you built it per plans (and could have a split bulkhead installed later that same day so whats the big deal) and that's on your conscience. Are all your tie-wraps exactly per the plans? Sheesh.
I know, I know, I know ... Regulation ABCDEF 123xyz.aabbcc blah blah blah get real blah blah blah
"A difference that MAKES no difference, IS no difference." -Spock