If you do a search in this section or perhaps the giant scale section, this was cover a little while back. A simple answer is yes, spoileron (also called reflex) will help with wing rocking in a harrier or elevator. What percentage will depend on the plane. Keep in mind though that if you intend to compete in IMAC, you cannot use this mix.

Also, have you tried moving your CG aft a little? This can sometimes help the wing rock.

What planes (size, company) are you flying? Perhaps if someone else flies the same set-up and uses spoileron, they could give you a starting point for the degree of deflection.

...........Mark