@jgThe problem might not be the mast but what is know as the backhaul which is the connection from the Mast to the Internet and Core network.
In some places and especially those either in deepest darkest rural areas and those at the coast the speeds of this backhaul cant sustain lots of users, and no matter what you do, unless councils allow them to put more masts up, or dig up roads to lay fibre cables then it wont change.
MicroWave Backhaul might help as well with this site.
5G and technologies such as OpenRAN will help this and some of the new LPWAN technologies from Nokia and Ericsson may help as well.
What 4G Router are you using? It might also be worth having a look at the ispreview.co.uk forums., as they discuss these things with regards to other networks and might be able to suggest some things to you.
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