Hello,
So I verified that on real parts.
Effectively, 15712 base has a height of 3mm instead of 3.2mm. Then I checked the location of the hook centre which is the important feature.
According to my measurements, it is locate at a height of 5.72mm. LDD locates it at 5.47mm.
From what I observed, 15712 and 2555 have the center of the hook both at the same location which makes sense as 15712 supersedes 2555.
for 2555, LDD models has the center at 5.68mm which is very close to 5.72mm that I measured.
On Mecabricks for both 2555 and 15712, I located the center at 5.80mm. I think I will keep this as.
The fact that it works in real life is because those distances are very small, ABS is easy to bend and stack of parts may have a tiny gap.
The fact that it works in LDD is because they do some weird things with modeling 😛

Wow, you sure can verify the parts to a high precision!

I really have a hard time understanding the clip and bar system, it's great for arbitrary angles but a nightmare if you have to use one for a 90 degree angle. Some combinations seem perfectly legitimate, others end up with unexpected fractional shifts. It's a pity that the 11 plate separation I mentioned is actually "invalid", I relied on that as the core of a MOC I've spent a few months working on. Guess I'll just have to rely on the flexibility of ABS and hope it doesn't actually damage the parts.

Anyway, thanks for checking this out!