I may be out in left field here, but are we possibly confusing the "taper" that you were reading about? I believe I have read the same thing but I assumed (there's that word) it was in reference to shaft end tapers for points/nocks and not for 10" of taper along the shaft.
If cut to length with point and nock tapers in place then you can not dip the whole shaft without also dipping your fingers or other item holding the shaft, which gets messy, and/or also leaving a small portion undipped because your fingers won't fit through the gasket. Therefore, dipping from both directions allows covering the point/nock tapers with less mess and without missing the little bit between the gasket and the lacquer. OTOH, if you have not cut your shafts to length and have no point taper in place, then you likely have a few extra inches to hold while dipping beyond desired length. This extra length allows for the "entire" arrow to reach the lacquer below the gasket. As long as the whole in the gasket isn't so large as to lose effectiveness I do not believe that tapering, say from 11/32 to 5/16, comes into play for dipping.
If I am way off base here then tell me to be quiet and listen and I'll be happy to learn something new.
I mostly use 11/32 shafts tapered to 5/16 and I cut them to length and turn point/nock tapers before any finish work. I use the gasket system on dip tubes and have no problems with Helmsman spar straight from the can. I usually dip six coats through the gasket always with the nock end down. My point tapers are long enough that I can hold the very tip and get full coverage with the tube filled nearly to the brim. The last 3/16” inch of my point taper doesn’t get urethane but it usually gets trimmed to fit in a point or it gets glued and covered before long. As Don noted above, cleaning the excess from the nock end after each dip is helpful. When dipping a dozen I usually can second dip #1 after #12 is hung to dry, but after 3 or 4 coats I wait a few extra minutes (as Don said above).
I've had good luck with this process. I hope your chosen method works well for you.