Always work on increasing your range for accuracy. If you develop your skill to accurately place an arrow in the kill zone of a 3D deer at 50yards, as an example, 15-20 yards becomes a cake walk.
As to whitetail deer, for me, reducing my range on deer has to do with the whitetails fast reaction time and ability to move at split second speed. Even if I could hit a tennis ball 10 out of 10 times at 30yards, I'm always concerned that the deer may drop, wheel around, leap, and then run off to parts unknown long before the slow stickbow arrow gets there:) At some point with experience, you'll get a feel for this and know when it is time to shoot or it is time to pass and wait. But, always push yourself in practice by increasing your range.
Best,
DB