LCB, I understand where you're coming from with the suburban/semi-urban sasquatch, it is hard to wrap one's head around how they pull it off. I think I benefited from the semi-suburban experiences I had in Colorado to prepare me for the Chicagoland situation. In that area, they were just behind the front range, hanging out in a canyon on the back side of a popular trail system. It was perhaps easier to accept, because you really only had civilization on one side, and easy access to vast wilderness on the other, but I don't think these were just little people-watching vacations for them. Similar to your situation, they would show up (I surmised) twice annually, once in June, once sometime in the Fall. If you put that alongside the Arrowhead Golf Course sighting, you can start to envision a group moving up and down the front range seasonally, and using the Platte River a lot.
That's not so different from what you (I think correctly) surmised about your group: they do laps around the forest preserves along the Des Plaines River, up to Fox Lake, down the Fox River out to the Seneca area. Don't forget the newspaper article on sightings along the Des Plaines from 1890 - these are not new routes, they are well-established.
All that said, I'm finding myself extremely dubious of the theory I was so excited about in the Spring: that they shortcut through the city somehow, that the odd little teepee structures that appeared overnight a few times on University of Chicago campus were them passing through. It's been a long time now since I've seen anything like that, and I'm back to thinking I was probably overly excited about nothing, but on the other hand, it's not something they'd do in the summer anyway. Also, I'm not at all dubious of my findings at Sidney Yates in the early summer, and if that's not somehow a through-route, it's puzzling why they'd go so far south on the North Chicago River if it's a dead-end.
Anyway, sorry if that was a bit rambling, but I guess I'm trying to say I empathize with the particulars of your frustration. It's an especially puzzling situation in Chicagoland. If you actually start stomping around off trail in these preserves though, you realize they're not as small as they seem. You'll also realize they're often swampy and gross, and you're the only one doing such a thing. Avoid the urge to underestimate them. And as you've said, you need to be ok with things being uncertain, even unknowable. That can be frustrating; it can also be enthralling.
Also meant to add, you should check out Chris Noel's "In the Micro-Forest" series on youtube if you have time