ideally, you want the large flat surface pointed forward and up, if you have it in your jacket, much like a phone would be, it wouldn't have the best reception angle and might not trigger.
Doesn't mean it won't work, or that you can't do it, but it doesn't only have to be on the windshield, anywhere else would work too, just the sensors are normally mounted above the gate pointed down and slightly back or to the side angled at the car rearview mirror, highspeed lanes they are above the lane pointed normally at a 45. Keep it away from metal though, as much as possibly, especially behind and infront of it.
Mountint it between your forks should work, probably not the best attractive option though.
Actually, my truck has a metal windshield, so it wasn't possible to mount it inside the cab/windshield, for that they had a external sensor mounted on the licenseplate bracket on the front.