Pls what is the present height you use at both ends.
Have you considered the height above sea level at both sides using your GPS?
so that you can do the necessary trade off in elevation for better LOS.
Fresnel Zone issue may be a factor here, raising your equipment over an appreciable height(like 10meters) at both ends
may just be the solution you have been looking for
for better results you need use at least 15m of margin over the LOS to assure the link.