Well, Alex, with the fob in front of you and the receiver behind and under you, there is a....er.....uhm..... LOT of material for those radio waves to penetrate.

A pants pocket would bring the fob closer to the transceiver that it 'chats' with.
KiPass fobs have a pretty weak signal to begin with- obviously adequate but certainly not an over- abundance. With my fob in my pocket, if I am standing in front of the bike and reach around the windshield to depress the key, the system just does not see the fob. I have to walk around to the side of the bike. So while wearing the fob around your neck is certainly well w/in the range of the fob, it is also subject to whatever metal you are wearing and metal is very difficult to transmit through. Belt buckles, change, metal zippers, etc. will all degrade the signal.
Brian
The issue I've had with my transponder is, I turn on the bike ride a couple of miles then I get the "NO TRANSPONDER" error. But it goes away soon after. Tried replacing battery but still happens. I wear my fob around my neck, do I need to keep it in my pocket?