Do you know the location of any other towers? Sometimes the closest one is not alwys the best one to aim at - this can be particularly true in rural / remote locations where the towers are often daisy chained together so the further down the chain you get the potential for more contention or reduced backhaul there is.
Trees, particularly ones with leaves on them are not insignificant sources of obstruction, leaves contain mostly water and that will act to scatter the signal so whilst you may not get much attenuation from them as a solid object potentailly the impact on the quality of the signal can be significant.
It is a decent enough antenna, data sheet claims ~6dB gain at 700MHz without cable losses (so probably closer to 5dB in reality) but yes you could find something higher gain. If you are looking for alternatives though you need to check the spec sheets and consider specifically the gain offered in the 700MHz band as that is what you say you are interested in.
A couple of options from the Poynting catlogue, Peplink does make a directional antenna but it is comprable in spec to what you already have.
Similar to what you have at the moment, slightly higher stated gain at 700MHz though:
Yagi style antenns, you’d want the SKU ideally that is sold as a kit of 2 antennas with the brackets required, on paper this offers considerably higher stated gain at 700MHz than what you are using at the moment:
How are you comparing the signal at each location you test at, what sort of readings do you get in terms of signal strength and quality?
These posts may help explain what some of the different terms are, and how they relate to each other:
https://forum.peplink.com/t/WAN-Quality/61adc18dfe2a1f568711032d/1
For a comparator point you could also use the included antennas that came with the 20X to see if the directional one is really making a good enough difference.
Are you able to test using another device like a standard cell phone or tablet at the same locations, does the performance of those suggest you should be getting significantly better results?
700MHz spectrum is in most cases used to deliver coverage and penetration through walls, not outright capacity, so if you are on a marginal signal / poor quality signal then you could be just at the limits of what that cell can deliver to you.