When we first installed the AG-NAV GPS on our Bell 47 we had to move the antennae back mid way on tail boom to get a signal. Not a big deal except in our business accuracy counts. We have our light bar set on 1 foot increments to guide us across the field while spraying. Our swath width is usually 35 feet, so, in a cross wind the further back the antennae is the more "off" a pilot can get. It's not enough to see unless you fly back over the pass you just made and have a ditch or ? for a visual reference. Two feet one way then two feet the other and you've got four feet off which can under some situations cause streaking in the field. We compromised and found a sweet spot that didn't hurt reception or accuracy (at least that we can tell).
Barry