Bob,
I had asked other builders to please repeat this test and report and I haven't found anyone yet that has. I've even asked several builders I've helped and they didn't do it either. I guess everyone is not as curious as I am but I wish someone would so we can get repeatability.
I did not separate the fuel tanks as they come from the factory already assembled and ready to install. The 12.0 lbs was both fuels tanks with hoses and all hardware attached to them as they would drop into the bay. The other thing that would add weight to that would be the straps that hold them in and then the larger fuel cover that goes over both fuel bays with extended fuel.
Obviously there is no way I could come up with a generic statement on unusable fuel since my last 2 airplanes have varied by quite a bit. That is why I do each airplane so I know what THAT AIRPLANE will do. Since I'm not going to go re-create the flight configuration needed to make the most fuel unusable, I'll just have to rely on what CC says and that is 39 gallons usable (5 gallons unusable) which is 1 gallon less than the same tanks in an EX2. Why the difference? I'm not sure. The rear spar is different on the EX3 and possibly the power difference in the CC363i will make a difference????? I have no other ideas.
What I do know, and the importance to me is that I KNOW if I'm low on fuel for whatever reason.....i will fly it level as best I can do until touchdown with the fuel selector on BOTH and I know how much fuel I need for it to continue to flow.
If you read on down in the post you will see my March, 2020 update on the last airplane I did which different. There was only about 3/4 of 1 gallon in each wing unusable (when fuel selector on BOTH) and I was actually able to account for the tanks and lines holding right at 44 gallons. So, essentially......I would ASSUME then that I can fly this airplane down to only 42.5 gallons before it runs out instead of only 39 listed.....AS LONG AS I'M FLYING STRAIGHT AND LEVEL AND HAVE FUEL SELECTOR ON BOTH.
Anyway, that's just what I've found.