@Andrew Lewis yeah, the physics absolutely backs you up here — antenna gain stacks on both ends so you're looking at combined link budget improvements that can be pretty substantial. The module's already doing a lot of work on receiver sensitivity and output power, but directional gain on top of that is essentially free margin you'd be leaving on the table otherwise.
The water monitoring example in that thread is a good real-world data point. 12dBi Yagis on both ends of a fixed link at that distance is a pretty solid choice — you're getting the gain where it matters without going overboard on beamwidth to the point where thermal expansion of the mounts becomes an alignment problem. For 30-40km on a fixed installation I'd probably look at panel antennas over Yagis just for the mechanical robustness in outdoor conditions, but either way the alignment discipline is the same.
One thing worth thinking about specifically with the MultiNav Pro+ is that you're already operating at a sensitivity floor that's well below what most BLE hardware can do, so the directional gain improvement will show up most noticeably in weather margin and link consistency rather than raw range extension — which sounds like exactly what your deployment needs.
