We’ve found you have to get the proxmark antenna right on. Like right ontop of the xBT and if you’re off by a couple mm in any direction it won’t read.
Finally, using lf search won’t work unless you change the lf config to 134kHz, but lf fdx read does work. But again, you have to get the antenna like directly onto the xBT.
We also have a Halo and we know it reads from like 2 or 3 inches away, so it’s very easy to work with the xBT with that. The Proxmark is waaaaay more fiddly in terms of antenna alignment.