The thing about RF transmission is the R squared loss.
If you get full bars or high signal levels and don’t see a tower, you’d better watch out.
In my kitchen, I get -81 on my iPhone 6. Ten feet away in the FR, laying on the couch, it’s -89. Yes, I can see a cell tower from my kitchen. It about .5 ~ 1.0 miles away.
iPhone field test mode code is: *3001#12345#*