Re: In-air mends
the timing of your upstream mend is critical on technical water, but it's not as crucial as the location of your cast. you already got a very good suggestion about trying to mend less line upstream. often times when we are having trouble with casting and mending, less is more. this is the counter-intuitive nature of fly fishing.
i have 2 suggestions along these lines:
first, land your fly further away from your actual target. this will give you more time/space to execute your mend without spooking fish. at least use this "cheat" until you get better at the cast-and-mend. i wouldn't work on an in-air mend beyond the reach cast, myself. i like to take the easiest and quickest path to my desired result. and that's not likely to be it.
second, work on making your mend immediately upon landing your fly. this requires line control. you have to keep just the right amount of slack in your cast...which is usually not much and certainly no more than absolutely necessary to achieve the mend. the goal here is to execute the mend before your entire fly line gets caught in the surface tension of the water. it doesn't take much mend, as has been previously stated. so this isn't as difficult as you may think.
personally, i've found this to be the best solution in about 90% of the scenarios in which i've encountered a problem with drag during an upstream drift. the same concept works with a downstream presentation, but the amount of slack and size of mend has to be much greater...so it's harder to do.