Your post said it was an omnidirectional antenna, but you also said best signal is directly in front of the unit. So at 180 deg, there's no signal? I'm asking because the only places I'm being allowed to place any WAP's is 5 ft up on a ledge that runs the length of the church, and I have to lay them flat so that no one sees them. 

-Hugh

The best signal is directly in front of the EAP245, the signal is much weak at 180 degree.

Maybe you can consider the outdoor EAP product, such as EAP225-Outdoor. The coverage degree of outdoor product is 360°, and the recommended coverage radius of EAP225-Outdoor is about 100 meter. You can refer to https://www.tp-link.com/en/products/details/cat-5693_EAP225-Outdoor.html

We did find a place in the church ceiling where we can hide WAP's. However the ceiling is 40 ft high (this is an old church) or ~=12 metres.  Do any of your products work as a ceiling mounted WAP where the distance is ~12 or so?

Thanks

-Hugh

The recommended coverage radius of celling EAP products are about 15m. I think the celling (12m) is much high for celling EAP product, it may cause weak signal to wireless clietns.

You can try to use EAP225-Outdoor. The antenna of EAP225-Outdoor can be rotated, it will help you adjust the best signal coverage area. (Try to point the antenna of EAP225-Outdoor to the place which you want to cover the WI-FI, it will help you get best signal strength)

Thanks Jonas, 

  I'll certainly give that a try.  I still have to climb up into the ceiling rafters to see what all we are dealing with :)

-Hugh

To sum this all up, we ended up going with the EAP 225 outdoor antennas, and I mounted 1 in each corner of the church to guarantee ubiquitous coverage, and to ensure that if we have 200 people all checking their facebook at the same time, we can handle it.  There were enough other bits and bobs on the walls in the corner to make the antennas nearly invisible (white on a powder blue wall), and only the most persnickety would notice them.  The 40 ft high ceiling made ceiling mounting unrealistic plus the access up there was precarious at best.

I will say that the signal on the outdoor antennas is powerful. My cell phone ends up picking up the WiFi when I'm outside across the street from the building where I installed them.

-Hugh

@jonas Hi and thanks for sharing this very useful information.
Unfortunately it seems like in my situation, I need more than 74 degrees. The ceiling is just 2.10m, and the room is quite wide.
1/ Is the 74 degrees number empirically tested / certified? it would make a big difference if this was for example 80..

2/ Is there a way to change the directional properties of the antenni ? (replacing them? bending them? placing something in front / behind the AP?)

3/ General question - do you know by any chance how much of a disturbance would Plaster and Concrete walls pose? (I may be able to gain more height)