Last year my pool store where I bought the pool told me to use an 8x15 or 2 4x8 compensators for 15x30 pool. I went with the 4x8's and over the winter one popped the other held fine. The popped one I guess Ice got it since it was sliced. So it did its job

I did buy a second compensator again but trying to decide the best route to go

1) is 1 better than 2 especially since I had that issue

2) On the 2 I just strung rope through them from end to end, a single rope. Into the winter after a storm the compensators slid to one side, both of them. I was debating how to tie these. Should I maybe tie the 2 together in the middle and then 1 line to each end of the pool. I did not secure to the end, just threaded under uprights in case cover got to heavy and sunk them.

Two is better. If one breaks you still have the other one. The exact placement isn't too critical, though you do want them closer to the center, rather than right up against the walls. Connecting them together sounds like a great idea.