Dear PCS,
I used to have a speed of around 3MB and had unreliable reception of iPlayer on a Foxsat, except on the lower setting. I have a much faster broadband now, and my troubles are over.
Have you tried campaigning for (much) better broadband speeds? I live in a small forgotten town where I had no support in this, definitely not from the local council and sleepy business group, but I contacted a number of people, including the local MP, and won. BT updated our local exchange earlier than expected which doubled the speed. Not only that, but I helped to push my town up in the queue for fibre.
It is worth considering optimising your connection for internet too. This should be your main one at the entry point to your house. I found it worth keeping the input to the filter as short as possible, ie connecting the filter directly into the entry box with any distance required (to reach the Freesat box) via a good quality RJ45 cable. It is worth buying this in CAT6 quality. You are allowed 10m on this but make it shorter if possible.
Hopefully this will be of use! Regards. IAINB