Eric wrote: I'm also using an MRX. I believe it's warnings are also
based distance and altitude trends, not just distance and altitude.
For example, consider two aircraft the same distance from you and the
same altitude above, one descending and one ascending. Only the
descending one will trigger the alert signal.

This "trend" clarification is a very important distinction. Thank you
for pointing it out. It helps to explain why sometimes aircraft are
within the MRX parameters, but don't trigger the beep-beeps.