The issue usually isn't the model, its that the prompt is asking it to "write well" instead of giving it clear constraints.
A few things that helped me, tell it to use plain, concrete language and avoid poetic or metaphorical phrases, explicitly ban filler like "imagine", "picture this", "heavy eyed", "journey", "unlock" etc. Make it explain concepts directly instead of creating atmosphere and have it write a first draft than run a second prompt that critiques and rewrites anything that sounds like AI or vague marketing copy. If you have examples of your writing use several samples instead of just one so it learns the overall pattern better.
For your example I would simply write, "This is the transition between wakefulness and sleep, known as the hypnagogic state, during this period your thoughts become less analytical and more associative making it easier to relax and process ideas, theta brain waves naturally occur during this stage as well as during deep meditation." Its much clearer and gets the point across without the unnecessary fluff.
Hopefully this helps