Improve the VHF coverage
 

Hi,
Hope I've chosen the right forum for my question.
I'm an Atsep trainee, And i would love to ask experts here about the ways to improve the VHF coverage over the oceanic part of the FIR ..
As you may know, VHF is "straight line" transmission and is therefore limited in range by the horizon. That is not a problem for as now for most populated parts of the FIR, but for operations in some oceanic airspace, you might be out of range of VHF stations.
For now, we succeeded covering 90% of the Oceanic part of our FIR for flight levels above FL300, where we have had less coverage, by implementing a new VHF station and updating old ones (make antenna directional, increase power, up to 200w ...)
But we still have problems for FL under FL300, because of VHF straight line transmission and curvature of the earth.
What do you suggest as a solution to ensure the VHF coverage for under FL300, and also if there are any other solutions for above FL300.

Hope I explained the problem well.

Thanks and Kind regards,
Abder

Unless you can change the laws of physics then it will stay the same. Satcom is the solution currently.