well I got reading into it abit more and I found this which gives a really good insight to it all;-
Antenna Selection Guide
I think the aerial that came with my kit was a 35dbi and by all accounts is incorrect for my needs. The higher the dbi the more precise the aerial positioning has to be , like a metal detector signal strength.
I'm going to dump the shitty aerial and go for a 12dbi which will give a bigger spread coverage width wise but a lesser distance.
There are 2 Three mast both within 2 miles of my property but in different directions (roughly 45 degrees away from each other) so hopefully the 12dbi yagi antenna will pick up a bit of both.
I've took a chance on this;-
17~21MHz 12dB 3G Yagi antenna with 1M N male Cable For booster/WIFI | eBay
make sure you check what MHZ and your provider coverage here ;-
4G frequencies - Which UK networks will my phone work on?