The typical U-Can-Do type(very fat with round leading edge) airfoil require a lot of spoileron,I use about 45Deg in the mix and have enough travel left over to have aileron control. I had to make some modifications to get this amount of travel on the Do. This helps a lot getting into the harrier with less rocking but you still have to experiment with each and every plane to find the right amount of elevator,spoileron and throttle setting to lock it in. The down side of using the mix is when you get into trouble, like heading to the ground and you need to pull up quickly,with spoilerons on,the plane does not pull up very well,in that situation its hard to hit the switch off first,I've bashed it a few times that way. I've noticed planes that harrier without spoilerons and had the chance to fly some for a few minutes,they all had more conventional scale like airfoils,thinner wings,more pointy,less rounded leading edges. Caps,Extra,Ultimate Bipe to name a few. My EF Yak would harrier w/o spoilerons but it seemed to require a lot of constant aileron input to stop rocking and lock in. I,ve only experienced 3 or 4 planes that didnt rock at all,harriers are so easy with them,but they werent my planes,they were:
The Monty foamy(TBM I think)
Cap H9 33%
Dave Patrick Extra 29%
Goldberg Ultimate.