For another kind of task, a colleague had written a very verbose prompt. Since I had to integrate it, I added some CRUD ops for prompts. For a test, I made a very short one, something like "analyze this as a <profession>". The output was pretty much comparable, except that the output on the longer prompt contained (quite a few) references to literal parts of that prompt. It wasn't incoherent, but it was as if that model (gemini 2.5, btw) has a basic response for the task it extracts from the prompt, and merges the superfluous bits in. It would seem that, at least for this particular task, the model cannot (easily) be made to "think" differently.