Making competitive range cut based on "reducing number of proposals for efficiency" - what's reasonable?

The few GAO protest decisions that address protests of an agency's decision to make a competitive range cut by reducing the number of proposals for efficiency all REDACT the exact number of proposals before and after the competitive range cut. I am trying to find out what GAO considers "reasonable" when reducing the range for "efficiency." Is 30 proposals cut down to just 10 reasonable? Is 20 proposals cut down to just 3 reasonable? What's reasonable?