Personally, I have always had some doubts about the supposedly greater depth of the Fo 987 on the Erla G-10 rather than on the MTT K-4...
The images available doesn't do much to change this impression...
This is the radiator on the K-4:
And here it is on the G-10 produced by Erla:
I cannot judge millimeters-wise, but it doesn't seem so different.
Maybe the difference was in width, due to the clearly different and more straight profile of the lower cowl designed in Leipzig...
I instead agree on the lack of consistence in quality and precision of the alleged MTT "technical" drawings, and IMHO, until original plans from both Erla and MTT will surface, every discussion could only be based on impressions and not true data.
Hope this helps.