I have a 2020 Stereo 160 Action Team in a small and have just fitted a 150mm fox transfer.
The stock one was the 100mm earlier version
If I remember correct, I had about 200mm from the top of the seat tube to the bottom of the post if pushed in all the way, the 'activator' sticks out about 30mm.
For my setup the original post had about 75mm of the seatpost out of the frame, the latest Transfer has a lower stack height so now only has about 50mm out.
There's a calculator on One Ups website that will work out the max length seatpost you can fit, conveniently it lists other brands as well as their own. Dropper Post Length Calculator
I couldn’t find anything to tell me the max insertion on my 2022 medium frame either. Managed to put the 150mm Axs in which has an insertion depth just shy of 250mm inc valve. The seat tube on the small is 50mm shorter than the medium but not sure that translates directly due to the kink in the seat tube.
If you look at the spec between small and medium the seat tube is 50mm shorter
If you look at the position of the rear Shock pivot, it seem 50mm closer to the top tube so I would say the seat tube is reduced on the small from the top
In case it's useful to anyone, I've just measured my medium size Stereo Hybrid 160 and the max insertion with a regular seatpost is 265mm. I've installed a OneUp V2 210mm which sits 18mm above the clamp at its maximum insertion. I'm 5ft8 and didn't even need to use a shim so pleased with the overall result.
I did find the internal cable routeing an absolute nightmare though, I ended up having to take the battery tray out and rerouting the outer cable because it wouldn't pull through.
So I’ve pulled the bike apart and got this picture of my 150mm Axs in a medium frame. Maybe 10mm clearance when fully inserted. Bottom part of this post measures 248mm with the vent valve.