Hi,
the settings can be tweaked based on your current observations.
If the queues tend to be busy more often than not (and your CPU usage is not high) it's likely that you're doing slow operations in your server code and you need a larger thread pool.
You can experiment with a larger core thread size (ex: 30-50) a backup size of maybe 60 and I wouldn't change the max backups.
Since you're creating 60 threads per backup --> 60 * 128 = 7680 threads, seems already pretty high. Unless you're running a very powerful machine with 10+ cores and lots of RAM.
Hope it helps