Gate opener antenna orientation
I'm not an antenna design expert, or an RF guru, but I did quite a bit of work with RF telemetry installations in hospitals using a similar RF band. I also worked with MRI RF systems, head/body coils, etc. 
Many factors can effect the loading of your antenna system, other conductors, metal fencing, etc. and something like that is probably happening here. If you have a spectrum analyzer you can tune your circuit to optimize the impedance, but I'm guessing that this type of equipment is way overkill for your application. Did you run A/B repeatibility tests to verify something else didn't change? You could probably have one person got to the edge of the remote range, and another person at the antenna, then communicating on your cell phone tune the antenna position for the best possible range. Then definitely fix it so that gravity, wind, etc is not changing the position of your antenna. Good luck.