I have a Zumo 550, my XM puck is attached to the top of the brake fluid reservoir with heavy duty velcro. No reception issues.
I have seen the puck mounted on top of the beak, I didn't care for the look.
1970 Honda SL100 (my 1st bike in 1972)
1972 Yamaha Enduro 360 (loved this bike)
1977 Yamaha RD 250
1978 Suzuki 250TS
1982 Kawasaki GPZ 550
2007 BMW F800ST
2009 BMW R1200GS (Current)