Apologies if this isn't the right place to post this

Trying to get my girlfriend and I NYC to TLV around August in J to visit family. Somewhat flexible on dates, best for her work schedule would be departing on a Friday and back Saturday or Sunday of the following week.

As an example, building a theoretical itinerary 8/17 to 8/21, I can select UA90 (departing 8/17) with an advertised "$4,211 round trip" (Z fare class), but the return in J bumps the round trip cost up to $6,555 (would be C class return). I've spent a while clicking around on the calendar, and keep getting the same results, I can find Z class to TLV, but not returning to NYC. All showing J9 in expert mode incidentally, so seems like they have the seats to sell.

Wondering if someone with better tools than I is able to tell me if there's a fare rule I'm either hitting or not hitting (like I've read there's generally a fare rule where you can get a lower fare if your itinerary includes a Saturday night stay, presumably there are other similar rules). The $4,211/pp round trip is about what I'd expect to pay, watching it jump to $6,555 makes me think I'm doing something wrong.