Mine is in front of the windshield on the cap, but I'm moving it under the cap up at the bow when I have some time. That only works on a glass boat though.
My current install is with 3M Body Molding double-sided tape. Has done well and no holes.
The 3ft thing is an interference issue, although I think what I've seen says 18". Some installs will work with the puck right next to the unit, and some don't. The LGC-3000 and 4000 are less prone to interference than the 2000.