I have consistently ridden in stock Dehner paddocks. Mine are 6" above the sole of the boot. I also have a old pair of Ariats, which are 7". Both are broken in.
Honestly, I can’t imagine how a half chap would “gap” in the back of the Dehner. I have used two different brands of half chaps and never thought about it. The most recent brand is the Ariat all terrain (also an older version). They are not really very “shaped” as other brands, and I still do not have an issue. My other brand was Grand Prix, fancier, with elasticized leather (but way hotter for Phoenix summers). Likewise, no issue there.
I have narrow feet and NO other brand paddock boot comes close to fitting me :).
I think the trick is to get the right size half chap, so you get the right length and a tight fit on the ankle. Good luck! I highly recommend the Dehner boots for their durability and comfort.