I’m not the expert on this, but a few thoughts:
- by introducing the mesh point, you add another device on your channel competing for airtime, and some packets may be directed via it; adding a mesh when it’s not necessary is going to make things worse, particularly when you only have 1mhz bandwidth available
- you use UDP and restrict the bitrate to 50kbps; I would have thought you’d get a higher bitrate than this, even with the restrictions you’ve mentioned. Did you select 50kbps because you noticed that this was the highest possible? Have you experimented with TCP?
- if you don’t need the flexible topology of 11s Mesh, it may be worth trying EasyMesh, as it will likely deliver higher performance for a straightforward non-LOS use case.
You may also find Why does adding each new node result in ~50% bandwidth reduction, even when stations are in close proximity? - #2 by swadsworth interesting, though it obviously isn’t exactly the same situation.