And we are in 100% agreement on this point.the only problem with mounting on the bike is if you depart the bike and need the SOS (which is the situation I'm most concerned with), you're out of luck. I keep mine in a jacket pocket and it seems to work well ... but your side by side test is very interesting. I view my Spot as an emergency communication device (SOS, etc.) ... the tracking is a nice to have addition but not the main reason I have it (even though I'm paying for the 5 min interval plan).
I am very conflicted about the bike mount and would prefer it in my jacket pocket or hanging from my jacket in some manner.
There are slots on the top and the bottom of the SPOT X that would allow for Velcro attachment points. I may end up at a local seamstress with a strip of Velcro and have her sew it to my mesh jacket. Not sure about doing that on my other jackets. But it seems to me that wearing it on my left side at roughly collar bone level could be ideal (assuming I don't land on it)