I did a similar exercise to you last year when considering buying a Poynting, or other antenna.
I also found conflicting results from those apps (ie. non-existent masts), so relied on lower figures (in the region of 40 - 60) from my smartphone when driving around to determine where in the general vicinity the masts were.
I found that the one closest to home - around 200m estimated, gave good enough figures on Telkom, so went with that. Later on, tested an MTN SIM, and speeds were reduced, but still acceptable. Ping was about the same for both.
I think if your antenna is directional, you'll literally have to have one of you in the household position it in a certain direction (on wall outside / roof ?), then another do a speed-test & see the results after each change in position. It will be time-consuming and irritating for the one moving the antenna around in all available directions, AND will be complicated by the fact that in your router, you should also be able to change from "Auto" to "4G only" to "3G & 4G", maybe "1800Mhz", "2300Mhz" depending on what it offers, and test each of those in turn.
This vid. gives some good info on testing (in the UK), though not watched in a long time :
How to increase 4G LTE Home Broadband Router Speeds
Hi, this video shows a 4G LTE Home Broadband Router and how you can increase the internet speeds. I will do a test using the internal in built antenna and then test again using an external antenna to see if the external one performs better.
As my figures were lower than yours, I didn't bother in the end, relying on only the internal antenna instead.
This is a good option to test with (if in southern part of the country, from PE West I'd think), as it gives jitter results as well :
Otherwise,
http://speedtest.co.za/ , or the one on this forum.
https://getvoip.com/blog/2018/04/02/understanding-jitter-voip/
Hope it works out, but I'm definitely no expert on this.