Glad to be of help.
Are you planning on using RF Elements? (I have been really happy with them so far.) (Though have not gotten the opportunity to use them with Mimosa Equipment.
Looking at the 40 degree beam pattern from RF Elements (the carrier class line) you will loose another 2-3 dB in signal to customers 2-5 degrees outside of the 20 degrees from center-line. Note: the 16.2 dB is only for the area that the pattern hits the 0 loss area. Every degree off center means you are getting less then 16.2 dB. (This is true for all antennas. Just less effecting to other types of antennas because you have sidelobes and long drop off lines where horns are really good at not having those.)
Here are some examples:
At 45 degrees from off center-line the AM-5G20-90 is loosing about 6 dB of the signal strength that you would see from being on the center-line. But that drops off fairly slowly compared to the RF Elements Horn
Using the RF Elements Link Calculator: (https://rfelements.com/calc/ it has gotten pretty good over the last year that I have been playing with it.)
At 4 miles the 40 degree horn will give you a -63 dB signal (if you are using a 24 dB antenna on your CPE) That drops off to -69 if the customer is 20 degrees from center-line and goes even lower very quickly. If you are dealing with noise at all it’s going to get pretty difficult quickly. Now all that said, you would get a bonus 3 dB using the A5c because of 4 chain MIMO wherever the signals overlapped, so that will help your MCS out a bit. But you will still need pretty big antennas on your CPE to keep up good signals.
Unfortunatly, RF Elements hasn’t released a 40 degree Asymmetrical sector yet and all of their Asymmetrical sectors are only Twist Ports for now. That said, I have been killing it with these new sectors and I would be tempted to deal with adapter cables and using a Twist Port to SMA deal to be able to use 2 60 degree sectors that would give you 17 dB to work with… The A5c gets overlap benefits as well.