Some like to fly inverted without any down in, i do not. Inverted flight with a highly aerobatic plane should just need a hint of down elevator. You will notice though if the aircraft isnt as responsive on rates as youd like as you shift the CoG back it gets more and more responsive and generally does knife edge, harriers and especially flat spins far better with a slightly rearward CoG. HOwever, I have never found the need to go rearward beyond the point where the model starts climbing inverted hands-off! Landings also then get interesting as they usually require down elevator, and flare is a return to nuetral and maybe slight up...very unnatural...