While I have tapped a few trees high to gain slope, it is not an idea that helps get more sap total. As you tap higher in the tree the internal pressure drops, thus less sap will be gotten from that tap than if the tap was at 4-6' off the ground. But then, especially those on gravity need to gain some slope just to make collection possible or faster or simpler, there you need to balance the facts with your situation to decide what to do. Even with 3/16, the gain from natural vacuum does not quite make up for the pressure loss inside the tree, but it does help.
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.