Antenna efficiency and PCB impact
Putting the antenna behind the board affects its performance.

Your board seems to contain a ground plane directly below the antenna, this can also adversely affect its performance, the ground plane in this case stops part of the signal from reaching the antenna.

The board size and layout also affects the antenna performance. If I am not mistaken, you have a monopole antenna from Lynx technologies (Or Laird, or Antenna Factor, same company), This antenna requires large (>10cm) ground for optimal performance.

If you can rotate the jack 90 degrees counter clockwise, you might get a significant improvement in reception range.