Interestingly enough, when I first got a three-ring (I started in the days of Capewells, and "graduated" to R-2's when I got my first rig), I practiced one hand on each. Repeatedly.
Then when I had my first cutaway, there were both of my hands on my cutaway, and both of them on the reserve. I guess since I'd trained originally to pull my reserve with both hands once I had a piggyback, it just went that way.
So ever since I've just assumed I'll do it that way, and I haven't disappointed myself, or bounced, yet. I'm one of those chesty women who can't see her reserve handle while arching, but it still just works that way.
Wendy P.