If I were you I'd put the y-harness on the elevators... if you think about it what mixes would you want on those? I mean you COULD do Ailevators which is where the elevators also act like ailerons. But the ailerons are huge and are in the prop wash so that doesn't make since.. Also If your going to run a Y-harness I believe the control horns have to be 180 degrees from each other..

On the other hand the Y-harness on the elevators opens up Aileron mixes, such as Flaperons (Both deflect downward but still can be ailerons) and/or spoilerons (Both deflect up, and also act like ailerons..

So go with the Y-harness on the elevators.. Regards. Cody