I had similar concerns when I moved to FTTP. In my case I moved from BT (which doesn't offer it) to Community Fibre.
These things helped me get the installation I wanted:-
1. Before the installation I did loads of clearing in the garage (where the previous BT came in over from the telephone pole as I wanted it though there and along the back wall and into my office at back of house. The man said there was space to go through existing holes all that way until we got to back of my office and just have one small hole to get it into here.
2. I came out several times to talk about what I wanted where.
3. I ordered Community Fibre's most expensive package (we get 5GB - very fast) which probably helped as they gave us three "child" units around the house to help boost signal - bit house 3 stoires, very very wide, all doors usually shut, very very sold wood doors and stone house including a panelled room I joke is the "Faraday Cage".
4. Before the man left I asked him to show me the signal in various rooms particularly upstairs. They were all within wha was promised. He rearranged one unit . As someone posted above it is not an exact science. We didn't test with doors shut but I felt he had done all he coud.
5. After the visit I accepted we would need to think about the issue of my adult sons working here from home often on Zoom/Teams calls all day in various rooms and various floors. I bought on Amazon a wireless access point and ran a cable from my office up 2 flights of stairs to that room in the middle of the house which usually has an open door as empty bed room. Then I ran cables to both sons' upstairs rooms so they can use an ethernet cable for their teams calls. One other adult child works here one day a week in the "Faraday cage" room and when she comes I put another ethernet cable just for the day from my office to that room for her teams calls. I then ran one into the big screen/TV room where the boys play video games and apparently that is now lightening speed to download anything once that ethernet cable is plugged into the X Box.
6. It was only when I installed the upstairs access point that my adult son in his bed room with no booster/child unit thing and no ethernet cable could watch youtube on his mobile in bed. At one poit he was sayig I had ruined the internet by getting the 5GB FTTP speed as it was worse for him in bed than the BT FTTC previous service for which we had 2 broadband accounts and modems and bills coming into the house - one in my office and one 2 flights up he would have used in bed before.
We are now okay although would not be without all the ethernet cables. Everyone always closes every door where they work or relax by the way and these are huge sold doors so it is not the fault of telecoms that it is a hard house to manage. It is also very very wide a house too not just high. The ceilings are very high too.
