It appears there are differences of opinion here about what "leverage" means. Jake and srm are correct about the physics....the righting line position doesn't affect the righting moment. However, putting the line over the hull gives an angle that requires less force (strength) for one to hold his body weight up just above the water...and it makes balancing easier. This could be considered leverage as well, I suppose. Therefore, if it works and is easier under the hull, do that. Otherwise, fling it over.

I agree with Karl on the ditching mast float if possible. If the mast is sealed and you can tolerate the occasional turtle, get rid of the extra weight at the end of that long moment arm.

A few strategically placed knots in the righting line can be very beneficial...a couple for hand-holds/climbing and one placed where your butt is just above the water when you hook the righting line in your harness and lean out. The harness carries the load instead of your arms. Then you can fling your arms back like a rodeo cowboy (for additional moment) or use them to properly deploy the righting bag. The bag should be on a separate righting line, as far out as possible (over your shoulder), and just above the water as well. The problem is that, as the mast comes up, you and the bag go in the water and your bouancy neutralizes the righting force, so you (and the bag) have to get up higher. You have to climb your righting line some, and a 3:1 purchase with camcleat on the righting bag line is invaluable.

For reference, I'm short (~5'7"), weigh ~ 175 lbs., and can right my Hobie 16 using the large Murray's bag without the wind helping. I've righted it without the bag a few times in 15 mph+, but wouldn't come close without significant wind assistance.