Sensors - not connecting. How to extend range?

I'm having issues with the range of the sensors within my home. Entry sensors keep disconnecting or registering open when they are closed. I've tried troubleshooting with the base stations moved around, however front and back doors are far enough apart, and through thick stone walls that either one is unreachable at a time. I understand the sensors work on low frequency RF, which typically works ok through walls, for things like my outside boiler thermostat controls. Is there a recognised way of extending the range of the base station or sensors? If not, Simplisafe, please develop something to deal with this issue. Otherwise this system is useless to me, and I presume many others.