I believe Vector by ai03 was just under 19mm in the front with a more traditional 7 degree typing angle. I’m not aware of many boards shorter than that, but any board with a Cherry lip on the front like Vector should feel shorter even if the overall height is the same. Other than that, I think you’re probably venturing into low-profile case or low-profile switch territory.
GEONWORKS F1-8X v2 has a front height of only 16.5mm (without bumpons) and a 9 degree typing angle.
It is currently in group buy phase and is not terribly expensive given the specs.
This may fit your low front height requirements.