you only switch the font so the distance between lines is determines by the size of glyphs + interlineskip .. best use:
\big \setupinterlinespace
My Problem is NOT the bad interlinespacing of the big font in my example. Of course I can correct that with your suggestion, but thats not the topic. These big font sentences are only examples for "elements", which are not set on the grid. The question is: How to achieve same distances between every normal text (set on the grid) and the "elements" (not set on the grid)? It is clear that not all before-distances and all after-distances respectivley can be the same simulatously, thats trivial. But at least all before-distances (so the distance between the text and the elements, in this order!) should be the same in the complete book. How to?