LOS and height will always be king. My area is very hilly/mountainous. A couple local node operators have surrepitously placed some solar nodes on mountainsides (which is public land); these nodes can reach effectively the entire valley in my city with LOS due to their height and thus carry the vast majority of all mesh traffic.

You cna sometimes complete some edge case connections by upping your antenna gain; going from a 3dbi omni to an 8dbi omni gives you a lot more link budget, at the cost of sacrificing the vertical range of the antenna making it worse in hilly/sloped areas. Antenna gain will never make up for poor positioning though.

I've even been toying with the idea of getting some 915mhz Yagi directional antennas and making a PtP out at my parents' rural property to see if I can get it online with the city mesh 30km away. But i doubt that would work with the hill issues we have- I'd have to sneak a solar node up to a 7600ft mountaintop and then deal with the winter maintenance headaches that entails.

Also, reducing interference helps. Try to locate the node away from power lines or other wireless transmitters that might otherwise generate some RFI and decrease the strength of received messages.