@highspeed 

I don't know how much vertical placement within the room matters, so long as you spread your units out to get coverage where you need it. 

I've got 5 units.  3 units are spread out on the main level, 1 is upstairs in the master bedroom, and 1 is in the middle of the basement.  

One sitting on a desk hutch (5' high), one on an entermainment center (3' high), and the other three are plugged into directly into outlets (1' high) using these brackets: https://www.amazon.com/gp/product/B07JD4QL49/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1.  

Singal is nice and strong everywhere in the house.

The nice thing about having multiple units is you can move them around a little bit and experiement with what works best.  For example, my upstairs unit was originally in another bedroom that is more central to the floorplan.  The signal to my bedroom was good but I found the speeds started slowing down (20Mbps in bed vs. 150-300Mbps at the door), so I moved the unit into my bedroom.  The bedrooms at the opposite end of the floor still get good signal and speed but from the unit on the main floor directly below.  You can use an internet speed test app and move around your house trying different approaches.  I use the free "Fing" app - works great.

@highspeed 

Here is a simple guide: https://www.tp-link.com/us/support/faq/455/

The only tip that does not apply is with the antennas positioning.