I was looking through the parameter list in the Mission Planner, and I noticed that each RC channel has a trim setting. The RC calibration procedure doesn't mention centering the sticks at any stage and I noticed that my trim parameters were different to my actual trim settings. On average my trim settings are about 1500 while the parameters were mostly set to 1200. However the surfaces on my plane are correctly trimmed when I put the plane in stabilize mode on the bench. 

I have also noticed in the forum that in loiter mode the throttle stick controls the altitude with center being maintain current altitude. Are the trim parameters just there for future implementation? My throttle trim parameter is just above the lowest throttle level. If I put my plane in to loiter mode will matching the trim setting (953) keep it at the same altitude or will keeping it centered (1498) achieve this?