Ah OK, so if a VM has 12 disks say, and they are split 4 per proxy, one proxy would act as the gateway for that particular VM backup and all the data would go through it? Almost as though the backup job is dedicating one proxy as a gateway for each one VM.
I can understand this approach when using compression, you're leveraging the CPU power of the other proxies, network probably isn't the bottleneck. In my case I have no compression enabled, so all I really want is direct to proxy transfers. I don't know if it's possible to get around this. FYI, the target is a SOBR, three repo's on three different IPs that are actually all sat on the same NAS, I'm trying to get 3Gb throughput to it (NIC bonding wasn't reliable enough).