Where in the IDW timeline does Frontiers happen?

Think along with me, because I really wanna find out. Oh, and I guess spoiler for who hasn't finished Frontiers or read issue #4 of the Sonic IDW comics

What we know is that the IDW series starts after the events of Sonic Forces. Makes sense. What confuses me is that moment when Sonic mentioned Tangle in Frontiers.

Sonic met Tangle in Issue #4, so I guess Frontiers happened after the Neo Metal Sonic Saga. When he mentioned her, he said "I bet Tangle would love to climb these ruins." meaning he knows her well enough to assume such a thing.

What I am wondering, was the Metal Virus Saga before or after Frontiers? I am hoping we'll get more info on that somewhere.

Tell me if you have an idea when it could've taken place.