leggy
Been here awhile...
As I pointed out in my earlier post, I feel there is a strong likelihood that what you feel is not related to tire flat spots. I believe it is a problem with the running gear or chassis. I have been following multiple threads on this forum for months and still can't find anyone who has clearly solved the problem by tire replacement. But I am still holding out hope . . . .
Could be the rear driveshaft/Cardan or the crosses that connect it. I had a car with vibration and noise problem at certain speed and got it fixed by replacing the Cardan. This is over 20 years ago.