....And you don't mind the approximately 50% loss (3.5 dB) in signal
strength due to the splitter? I don't want to figure out how that
affects detection range.

snip

I have an antenna splitter installed. First antenna is a stripe antenna in the canopy (laterally & slightly behind my head), second antenna is the standard lambda/4 "toothpick" by the gear door. The Ventus cM is all carbon, and I have 5 km reception all around with a Flarm 5.

--
Dan Marotta