Your design is correct.
It is not supported to have a different MAC on the multiple paths.
It is kind of explained here https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/guide-c07-743150.html#LogicalInterfaceProfiledetails
"This is a MAC address for the subinterface, routed interface, or SVI. In most cases, this field can be left as the default. Changing the default MAC address for SVIs and, potentially, subinterfaces is sometimes necessary in order to prevent MAC flaps on an external device. This is because ACI uses the same MAC address for any interfaces, by default. For example, when two border-leaf switches are connected to the same external device with the same VLAN without vPC, the external device will see MAC flapping between two border leaf switches. This can be fixed by giving a unique MAC address to the SVIs of the different border leaf switches."
The scenario where you would want to use different macs would be if the same encap vlan is used on multiple paths, AND there is an external l2 path bridging those paths together
^I would argue that's a really bad design though since we are already extending the vlan through aci...never good idea to have both an internal and external l2 path extending the same vlan. STP would have to block paths or you would have a loop.
