I am a big medieval history buff and started collecting the Schleich figures some time ago.
I have two of the castle sets and almost all the accessories plus a pretty good compliment of the various soldiers, yeoman archers, plus both mounted and unmounted knights.
All of the Schleich standing figures are all about 3.5 inches tall, which might make them more in the range of 1/19 or 1/20 scale. The big difference is that they are proportioned a bit broader or thicker bodied than the XD figures are. Their heads, limbs, hands, feet are large compared to the more anatomically correct XD figures, so it is really hard to even get a sense of the true scale.
They are all packed away right now, but below are some pictures taken when I had them set up with the staged figures all around. The castles probably would work OK but be on the smallesh side of the 1/18th stuff but it would be way to large for the 1/32nd.
I do have some of the medieval figures on display, so here are some of both the Schleich and the XD figures side by side. The knights are closer in height to the smaller XD figures that came with some of the early planes and tanks, but much shorter than the Artilleryman that came with the Pak 40.
I hope this helps.
Cheers