@CM_Stewart I now follow the point about drape as being some slack in the system. I always felt the most critical part of the slack in the system was at the tippet end. Not only must the tippet be long enough to have enough slack to drift naturally but it also must have enough slack for the fish to hold on to the fly long enough to even get us to the point of seeing the “drape slack” taken up. So yes while the drape is a type of slack, we are still holding LL off the water and in the air…so it has a tension to it…granted not the same as the rod tip but a tension that a fish must pull on for it to go straight. So the question is does the added slack via drape in a heavier line with that line having added weight and therefore more tension needed to pull it straight actually lead to a fish holding a fly longer? Sounds like you are convinced. I am not. But the topic is for sure interesting and has me thinking over some of these concepts more.
As for strike detection, I watch either my knot at the end of the LL or a small section of sighter there for movement. Obviously that is removing the drape, I just don’t think of it as watching for the drape disappearing or line straightening I think of reacting before that while in reality I am sure I am slower than that. I have sometimes found that quicker tension is why you get the hook set as the fish partially hooks himself. I also wonder if the drape difference between 2.5 and 3.5 LL does buy the average angler (given an average human reaction time) a markedly greater amount of time to react - or would that weight difference need to be bigger?
I still think I would choose my line based on other factors first…but perhaps in specific circumstances it is more of a consideration?
I manipulate the fly all the time when I fish upstream of myself…maybe that is a beginner move…I don’t know…but it is fun. I like to cast into plunges and moments after the fly gets taken down pulse the fly. I sometimes while drifting into what I feel is a prime lie “lift” the fly like it is emerging. I also often cast upstream near a bank or under cut bank and pulse the fly away from the bank…they all work at times.