I've never found a simple formula for pursuit that works for me in a barrel roll/rolling scissors/barrel roll defense. What I do is adjust my pursuit based on my needs at the moment. I may need to pull
lead pursuit to fall
behind my target...
I'm not consciously thinking lead/lag/pure while I'm maneuvering, I'm just intently watching my opponent and flying to a place right behind him, and using whichever pursuit curve I need at that moment to do that, and I'll change it by the second if I need to. I'm using the barrel roll "offensively" from a defensive position. I'm not using it to dodge getting killed, so much as a tool to get behind my opponent for a shot (which means I need speed to follow, maneuver, keep my opponent in guns range following the roll. AT the top, I often just roll, with no elevator at all, but a whole lotta rudder.
A few tips-
Keep your speed up, but "reasonable". Don't get super-slow. The barrel roll doesn't work by flying slower than your opponent, it works by flying a different path than your opponent. You have more choices when it comes to doing that if you have reasonable speed.
Don't just do a barrel roll in front of your opponent, because you'll be an easy target. Get him coming from the side, at least a bit. Or even from the front a bit, if you can. It helps fool him into rolling with you, and makes you more tempting.
Keep it brief. Do your barrel roll in such a manner that you don't need to use 3,4,5 of them to get behind the guy. Try to be done with that stuff after a roll or two. Be more aggressive with your first roll.
Here are a few clips of barrel rolls. Watch it from my views to see how the pursuit mode changes. It's hard to describe, easier to see. Lots of different rolling scenes.
http://www.4shared.com/file/rVA77Rz8/DREDLOCK_190D9_BRD_and_RatCH_N.htmlhttp://www.4shared.com/file/wuxWi7MV/P38_overshoot.htmlhttp://www.4shared.com/file/I27fUfmx/Shawk_1A_vs_1A.htmlhttp://www.4shared.com/file/h-4VeyW-/Good_fight_with_Solar10_1259.html