Hi there
I've generally found the numbers useless or confusing other than "my leaders are so long" and "tops longer than bottoms" so I've tried to cross reference that with what I see in videos and pictures since I've had no read reference as to what the 'normal' differential is.
I must add that the 6 inch differential was on new leaders on my full vent. I'm guessing I should be able to go a bit further on a full sail. My top leaders in this case are about 9 1/4 inches from the last knot to the handle clip and the bottom is only 1 1/8 inch.
I understand the tuning theory but had no markers or points of reference to assess where I was. Its well and good explaining the theory, but without markers I've just been guessing ... And without anyone with a good setup for a reference, I'm in the dark.
I like your flight characteristic reference as well, I'm going to give that a go next time out. I have found that I fly better with the bottom 3 fingers forming the grip and the index finger loose as opposed to the other way around. This may be in part due to the fact that I have smaller hands than average so for my thumb to rest where I want it my hand goes higher. It could also likely be due to other training I have in a completely different area that has the bulk of the grip and grip strength on those fingers.
Whatever the case, I feel I fly much better that way and technically I can still apply the 3 finger differential pressure technique.
Steven