We use the Ubiquiti In-Walls and are satisfied with the results. In this situation simply add another to improve coverage the difficult area.

I always tell customers that an In-Wall behind the sofa does not offer the same coverage as a mega powerful ceiling unit, however, an access point in each room is more effective than the mega unit down the hall around the corner, or on a different floor.

The current In-Walls are better than the original. The originals could get into trouble if someone connected the wrong client to the PoE output port. I usually use the HD or Pro. The radiation pattern of the lower unit is more uniform if you want to attempt cover a larger area, but in my opinion, In-Walls are not the correct approach for wide area coverage with a single unit.

We also use Eero when wiring is not an option. The Eero Pro 6 is interesting. Obviously, we don't have a lot of experience with the Pro 6 yet. Installation is quick and easy, but you have boxes and power supplies scattered about. In-Walls are clean looking.

Overall, I'm finding that WiFi6 is more effective than earlier incarnations. This is partly because WiFi6 is what it is and partly because the newer designs are more effective in any case. Whenever practical I steer customers toward WiFi6.