remotes for 2 TVs within close proximity

I have 2 TVs that were installed in a kitchen, both are on seperate boxes but within 6' of each other.

The TVs as well as the boxes were installed by professional installers.

The Problem; 1 remote only works 1 TV (as is is supposed to), the 2nd remote works both sets unless you are standing directly in front of the TV. The remotes are both RF as the boxes are located behind the TV.

The installer is trying to sell us expensive after market remotes and after the fact has told us that there is no way to make each remote only work 1 TV.

The question; how can the DirectTV remotes be programmed in order to operate only 1 TV set at a time?

The boxes are small and I have been told that they are the latest most advanced available.

Thank You.

Tim