At what point do you call a riv bet HU w. A high?

Lately I have been calling down w. A high in giant pots quite often. Some hands I win, but more often I lose. My rule is usually that if I am getting 10:1 on my call I will do it. Is that too low? Should I increase it to 12:1? 15:1? I don't know if this current play is making or losing money for me. Anybody have some feedback? Thanks