For the KE mix I use the low rate part of the ELEV. I use three different rate switches. One each for AILE,RUD,ELEV. A rarely use low rate on ELEV. So I put the mix there. The trainer switch I use for the spoileron mix. I think you will find that this changes for every flyer. What I am comfortable with you may not be. For example. My best flying buddy uses one three position switch for his rates. His AILE,RUD,ELEV have three rates but are all on one switch. He has his KE mix on a switch that he is comfortable flipping. We also both use fuel tubing. I have have a piece on the AILE and ELEV switches. This makes them easy to find without looking.
BTW we both use a 9C. The radio you have could make a difference in the set up.

David