Why is my video output squished horizontally?

[CRTin4K]

After years of wanting one, I finally got a working X68000. However, all of my games are squished horizontally. I'm using a Sony CPD-1302 tri-sync monitor which is capable of displaying all three video modes, but the majority of them don't fill the screen even with the h-width pot maxed. Does an original Sharp monitor just offer an absurd amount of horizontal width adjustment? The only games I've found so far to fill my screen are Mahou Daisakusen in 15khz wide mode, and Akumajou Dracula in 15khz mode.

Is this something that can be fixed? I'm so excited to play this thing but it certainly doesn't seem right like this.