Looking for an OEM drop-in transceiver capable of 2 miles

My end product design requires that I am able to transmit/receive short amounts of data at random intervals. The challenge is, this will not be line-of-site, with the 'client' transceiver(s) varying from ground between 1 and 4 feet.

I have ran experiments with a few commercially available units with expected results. Both are in the 900Mhz unlicensed bands, limiting my total power to 1W.

My results ranged from 100% data pass up to 1/2 mile in different terrain, up to 1.5 miles with varying data pass rates. (10% to 60%)

My antenna on the base included both a 2dB dipole at 6ft off the ground, to a 4 position YAGI (8dB) at 15ft (and many steps in between)

My results I suspect are very typical. However, before I integrate into the final design, I feel I need to do some more looking. My customer really needs more distance in non-line-of-site conditions. I don't want the hassle of a scratch design (no budget really either) but my customer doesn't mind if a 'license is required'. However, I can't find such a beast.

Any ideas?

Line-of-sight propagation requires a path where both antennas are visible to one another and there are no obstructions. And because you have UHF communication (VHF is pretty much the same) you need this path ..
1W output power for 2 miles distance is more than enough, so increasing output power wouldn't change anything ..
So, what's left?
Ground-Wave Propagation? or Sky-Wave Propagation?
No ..

I think you should consider significantly higher antenna mast ..

Regards,
IanP