One idea: if the casing was a little too wide and overlapped the top of your window, it could partly or fully conceal the top of your blinds, kind of like a soffit or valance (I think that's the word for it). It would actually make your blinds look better.

However, consider a couple of things: you will want to widen your windowsill so it's in balance with the new casing. And also: make sure those blind brackets don't get trapped in -- somebody might want to remove them in the future.

Thanks so much for the suggestion! I hadn’t considered overlapping the top of the window, but as I think about that I believe that would probably be the best solution. I don’t think it would impede the brackets either. I’d be using standard door casing of 2.25” width, so it’d only overlap the blinds by roughly 3/4”.

As for the window sill, another question for you. If I keep an eighth of an inch reveal I’ll have a little over 1/2 an inch gap of sill after the casing is installed.

Would I still need to widen the window sill or am I fine with 1/2 an inch on both sides?