Try adding another 1/8 turn to the truss rod. It sounds like it's getting tight. Not a big deal, just make sure your wrench is in good shape and fully engaged. You can also loosen the strings to slack so the truss rod doesn't have as much tension working against it while you're adjusting.
As a last resort, your tech can order a full-contact tapered neck shim from us. They are CNC machined and laser cut. Very precise.
Edit: I just saw your photo with the rule measuring relief. That's too much. It's not likely the rod is maxed out but it may feel very tight. Have a tech take a look.