To further confuse you --
some radios -older ones do NOT match the outgoing signals to the elev and the aux channel - bad setups
these will never match.
the best newer setups such as the 9303JR have a built in elev/aux setup you select the radio to kill any switch involvement then select active elev and extra channel - NOW the radio shows a left elev channel and a right elev channel.
IF you do your geometry exactly the same for each side (as noted above)- you will get things as good as possible allowing for slop/ internal component differences etc.
So - the matchbox can really help if you have a radio which is a less than perfect setup -- but it will never correct for lousy geometry.