back about 2004 I made my drops 24", I later went to 28", then 32" and now 36". I see no reason to keep the tap within 6-8" of the tap hole. You want the drop long enough that you can reach completely around the tree in one direction or the other so you can tap where you should.
You should realize that if tapping without vacuum, you want to tap 2-3" to the right (or left) but always in the same direction year after year and tap up or down about 6" from the previous year. If on vacuum, figure a pattern so you tap at like 12 o'clock yr 1, 6 in yr 2, 3 in yr 3 and 9 in yr 4, then in yr 5 about 5, then 11 and keep working in a pattern like that. If you use longer drops you have enough to cut off last years tap and add a new one. When the drop gets too short, replace it with a new one 36" or longer.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.