I have two quick questions regarding russian dips:
1) I mastered these a while ago, but I've gone back to try and slow them down even more and develop more strength in the MU. The apparatus I've been training them on now is a captain's chair leg lift machine at my local gym. The set up is such that, when in upper arm support, my lower back and part of my upper back are inevitably contacting the back pad of the apparatus and it's providing some back support. Would this make them significantly easier? I've made a ton of progress on these since the last time
I trained them (on p bars, no back support), and it just dawned on me that the back support may be making them much easier and I haven't actually gotten that much stronger 
2) I'm helping a buddy of mine develop his L-sit MU on rings. To do this we're working on L-sit false grip pull-ups and L-sit russian dips--the technique that worked for me. However, he can't seem to transition well between regular russian dips and l-sit russian dips. I can think of three methods to bridge this gap:
a. Doing negative l-sit russian dips.
b. Doing concentrics of tucked l russian dips.
c. Increasing the difficulty of regular russian dips by either REALLY slowing them down or weighting them.
Which of the above do you all think would work best? I didn't have much trouble transitioning from regular to l-sit, so I dont have much advice to offer.
Thanks for the help! 