Nexus VPC design question?

With normal stack wise and VSS they use one control plane each for when they're stacked together and packets that need to travel between the switches in the stack go over either the stack wise cables or the VSL link. With Nexus, the peer link will only be used if no other link or way of getting to a destination is possible.

So with a back to back VPC setup, if a packet comes in upstream on a VPC portchannel that spans across all downstream switches and needs to go back out on that same downstream portchannel to the other downstream switch where the destination resides then it wouldn't because its not allowed since packets received in on a portchannel do not go back out the same portchannel interfaces. So would the peer link would be used? And if so, then once it gets across the peer link the other VPC peer switch would forward it out the same VPC downstream possibly the wrong interface in the portchannel because that's what the hashing fell on, providing a 50% chance of sub optimal forwarding?

So singled side VPC were a seperate VPC is on each of the upstream switches and is used to allow a packet to go upstream to the upstream VPC switches and then back downstream onto the other VPC portchannel interfaces that the destination resides on. Is this right or am I missing something?

Apologies if the description is confusing but it makes sense to me haha.

Thanks everyone for the help