Yeah, you need 'minimal' air... 'just enough' to raise your butt off the seat. A quarter inch would do. Funny though... when you do, finally get it 'dialed in', you would swear (to look at) that it isn't inflated enough to be efective.
You say you get a floating sensation... too much air dude. Let some out. Keep adjusting until the floaties are gone.
Watched a YT vid on the Airhawk R and the reviewer basically said to inflate it to required firmness... LOL, that's not how the Airhawk works. Has nothing to do with 'firmness'. As mentioned above... keep letting air out until the floaties are gone, but with 'some' air remaining. That, is Optimal inflation.