The OS selects network services based on the network adapter preferences in Control Panel / Network Options / Advanced (Menu) / Advanced Settings. The item highest in the list will always be the adapter that sends your outgoing traffic, even if you do hard code multiplicity to use the wireless address. If you really want multiplicity to use the wired connection you'd need to promote that one to the top and use that adapter's IP address in the Multiplicity configuration on the primary, otherwise it sounds like you'll be splitting incoming and outgoing traffic across adapters.