Most mode S have a XPDR mode.
XPDR which is the old mode Alpha with just the number being squirted but with some mode S trickery which means you don't show to aircraft in the air. Well at XPDR airports I never see anything on the ground on our honeywell.
RA is turned off below 1100ft rad alt decending and turns on again through 900ft climbing.
We have another installation where its just on and off. Apparently it does the XPDR thing with ground air logic maybe your jet is the same.
Must admit there seems to be some awful SOP's out there for TCAS and what to select when and what ranges etc and up down and normal. Most dont actually change what it does, just seem to be a beating stick for picking fault with people who really don't care what its set at but will do as it tells us when triggered.
The unit which is just on off is by far the least hassle it has one fixed range of 10 miles and no up/down selection. You just turn it on and leave it alone.