Hornstein seems to be trying to encircle me, but they're not doing a great job - their supply lines are stretched thin by the terrain so it's been pretty easy to prune back the overextended would-be flankers. They've managed to get one or two breakthroughs, but they've been on the edge of the front rather than in the center, so they haven't been able to reinforce & exploit them and get killed off fairly quickly. They were doing better at the start when I had mobilized fewer regulars - they outflanked and overran my half-militia battle line, pushing me back to the hex adjacent to the zone capital, but at that point I managed to I stand up and deploy two full Long Term Planning Workgroups (with defensive postures and a literal handful of my most modern light/medium tank units in support slots). Their advance stalled and I managed to gradually build up enough regulars to start pushing them back after that. They tried to push through my lines a couple of times, but had heavy losses every time they did - my (now-last-gen, but at the time modern) troops outmatched theirs, and we were numerically equal, so it went rather badly for them. They also stopped trying air attacks after I deployed small amounts of AA. They're switching to light & medium armor formations, but the LTP unit model has done fine handling those too. I was worried a couple of turns ago when I first saw they'd started deploying poly-armored tanks, but those haven't fared much better. Oh, and they've also deployed a couple of indy buggy brigades - those haven't held up well against concentrated attacks, but have probably done more casualties to me per buggy lost than their tanks have (mostly b/c they're hitting my flanks where they're only fighting 1-2 BNs at once).
Overall, I'd say they're very cautious - they don't want to attack if it's gonna get them killed, and I haven't given them a lot of openings where they can avoid that (mostly b/c I've felt like any recklessness will cost me these isolated two zones). They're not folding like majors used to; the advances I've made have been after pushing back their lines (and they pushed my advances back once or twice in the process). The biggest avoidable mistake I've seen is a failure to use postures well - the AI sets postures on its units and never changes them, so I've been able to use troops in a defensive posture safely & effectively in offensive actions b/c Hornstein troops are defending in an offensive posture or even Field Training.