It really isn't any harder to roll a wider kayak, I've rolled my 28" wide Dagger Approach lake boat with the same amount of effort as in my Jackson Hero. It's all in your technique.

 

First, one must find his inner peace, Grasshopper

 

Some boats are infact easier or harder to roll but the reality is the technique is the same. Some boats just let you get away with less precise technique. Work on the basics. Slow it down to really highlight your problem areas. Paddle at the surface, work comes from the hips head down.

If you're struggling Eric Jackson has a decent video on rolling a bracing.

 

Video tape yourself rolling and play it back. The 8.6 is one of the easiest boat out there to roll. IMHO.

 

Want to know something funny? I have a harder time rolling smaller/play boats than something bigger. My XP9 and Solo Expedition I can roll easily...inertia, I guess...which might answer your question on what it takes.

 

I agree that it's all in the technique. It's not actually that hard to roll a ducky and that's a lot wider than a mamba.

 

It's about a good setup. Often people sneak forward while setting up, rather than keeping their head directly off their hip. The closer you can keep your head to your hip, and the closure you can get your head to the surface on your set up should help you roll anything.

 

I'm serious...
By "inner peace" I mean to set up in your roll position, wait until you feel a bite on your power face, then quick roll while you have something to pull on.
Simple...
Howyabeen Jim I see you there...

 

How's your offside roll? I think being able to roll both directions limits the amount of "oomph" you need to provide. In any given roll situation, one direction will usually be easier than the other. By rolling on both sides, you'll develop some intuition for which direction is easier, so you'll be able to go with the flow!