Might be a bit late on this, but ProxMox doesn't really handle assigning threads to the e/p cores. That's handled by the kernel and as long you're running kernel version 6.1 or greater you should be good on that front.
If you really need to, you can also pin specific VMs to specific cores. So that if you've got something that always needs the performance it can always run on the p-cores and things that aren't as demanding can always run on e-cores.
That said, especially if you're over provisioning, it's probably better to let the scheduler in the kernel handle thread assignments.
