I know that I am on the limit...and having at least 70m cable with a "4 input" disecq...sure dont help...
Let me start with some congrats on getting a good result. Always good to hear from people with some positive results.
Then - just want to repeat my earlier comment - please note that the 70m of cable is not the biggest challenge.
If reasonably undamaged, and not running close to power lines and faulty microwave ovens, they will just give a lower absolute signal sttength to your receiver.
Not lower quality.
The C/N ratio is what matters - and this is large determined by:
1) dish size - as A33 writes yours is really a 105cm. A true 120 (usually 135cm tall) is 30% bigger surfacewise than a 105, giving more C/N to work with
2) LNB accuracy and feedhorn match to dish - some are much better than others. The Inverto Black Ultra are quite good, so does some Octagons and Maximum seem to be.
3) Antenna alignment. Getting especially 28.2E to line up takes some effort, as the 3 sats are spread out from 28.2 to 28.5. Aligning must be done to point to the best compromise between SD and HD channels on 2E, 2F and 2G.
My point is - going from 3 to 1 - you can fiddle with the alignment to balance reception of 2E, and 2F/G. This is low cost high-effort.
Next up is trying better LNBs. The one you have might be very good for the Astra 2 challenge, or it might not. Only some experimentation will tell. And some dosh to buy a few LNBs. But lower effort, as the dish is already aligned.
Finally, as mentioned by others, get a bigger dish: A Gibertini 125 (which is really a 120), an Andrews/CM/ASC/Raven/Skyware 120 cm (which is really a 120cm), or a current popular dish is the Laminas OFC1200, which is again a 120cm dish. But these are more cost, and needs re-aligning all over again.
So - if you are happy now (and it seems that way) - enjoy UK TV.
If you want more, try replacing LNB with a Black Ultra (don't get confused by similarly named LNBs. Must be an Inverto Black Ultra Single/Dual/Quad.)
Step 2: Call the installer back and have them re-align to favour high FEC 2F/G signals, by compormisisng somewhere between 28.2 and 28.5.
Step 3: Get a bigger dish...