RAK7258 Multi WAN Config

Can someone confirm that in the RAK7258 multiwan config, if the primary interface goes offline (eth0) then the cellular jumps in as secondary, once the primary comes back online does the data path revert to primary, or does the secondary then need to fail before it reverts?

I’m looking to utilise a 4g sim card for redundancy, with ethernet as primary, but only need a very small datapack, as the ehernet link is reliable. But if it doesnt fail back, then i’ll pay a high penalty for exceeding the dataplan.

What I thought would be a simple test has become a struggle to test confidently.

Thanks in advance