When I was controlling (military) in the UK Upoer Airpace (above FL245) it was a mandatory control environment. So everyone there was being controlled by someone. Ergo, anything below 245 was just screen clutter, and thus on the T-82 radar we could operate in "Beam 6" and thus filter out all the medium and lower level stuff.
Drop below 245, and we would operate in "All Beams" to ensure we saw any possible conflicts. Then, if needed, we would use the height finder to determine the height if the conflict ... 5.000 FT vertical separation being required.
Any SSR data was a bonus, allowing coordination with the relevant controlling agency (if showing).