Cactus Flyer,
I used elevons and my new model likewise. It would have been difficult to get thin enough servos in a good position to drive outboard ailerons.
I would say that your elevator to flap mixing ratio is a good starting point.
BTW, if you have a slow function, use it on the canard flaps. They also work as elevators quite well. In fact, for particularly short runways I mixed down flap with up elevator in take off mode. This was as well as some flap set in this mode anyway. It would rotate the model at a ridiculously low speed. The Viggen properly set up would not stall in this condition, just rock its wings a little.
Regards,

john.