I use a cardholder. And my CEPAS card is always the first card
in the pile, and there are no other RF cards in it. So there's only
a few microns of PVC between the card and the sensor.
But some occasions, I've had to friggin' slam the card down onto
the sensor just to have it read. 
Once I was in a rush..... I tapped the card and tried to run
through the orange gates, thinking it would be open....
I ended up slamming my abdomen right against the closed orange
gates.
Luckily I didn't get slammed anywhere lower.....
stop short of a total malfunction, don't think you've an excuse
to exchange it. maybe you really need to slam it down
