Basic principle, guys. Any satellite service, GPS, Sat Radio, etc., requires an unobstructed view of the sky by the antenna. That's just the way it works.
When I had the sat radio on the bike, it worked flawlessly. The shortcoming were the speakers.
You might try to place the puck on the top of the ignition switch cover. It might fit there. I don't know how big the puck that comes with the Garmin is but the one I have would fit there. I have a Corbin fairing so that wasn't an option for me.