I've written PC software as well that can pick up Garmin ANT hr strap data using an ANT USB stick.
And I've noticed that the transmission is unsteady, lot's of drop outs. The distance hr strap <-> ANT stick shouldn't exceed approx. 1 meter.
So the ultimate solution might be an USB extension cable
Perhaps you'd say "but my Garmin xyz picks up HR smoothly!!!".
I'd respond: "Who tellya dat??"
The Garmin gives you the impression of a non-interrupted hr display. But I'd bet that they swindle and wave the white flag no sooner than after almost 10 seconds of communication dropout. You can easily try it out.
Cheers,
OMB