The "Trim Mix" has nothing to do with trims. It is a means to offset the trailing edge (ailerons and flaps, or flaps alone) a given amount at the flip of a switch. Having said htat, if you have found a way to get the radio to do what you want it to in a way your want it done, then you have achieved your goals.
I use the methods I outlined to get my gliders and power planes (warbirds and scale planes) with flaps to do what I want them to do. This is the real power of these radios. There are many ways to achieve your desired outcome.