You can get over kill on scope power at extended ranges. What you have out there is mirage. The high power scopes will magnify that mirage washing out the target. Of course every one's eyes are different but for me, in using glass in 1000 yard matches, I found the 10 X to be the best (again thats me, your eyes may be different).
When we shot team matches as a coach I used a 100 mm spotting scope. The scope came with a variety of eye pieces, 16-32X. I found the 20 X worked best for seen the trace and mirage.
Another problem with the higher powered scopes is heat coming off the barrel. You see this, and it interferes with your reading mirage.
Even with the 10X scope I use a barrel ban to break up the heat waves coming off the barrel.
Even when using the 10X scope, I had my spotting scope next to me for reading mirage and other environmental conditions.
Like I said, this works for me, everyone's eyes are different.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071