I like how many things can be tuned in the GUI of kate, but I miss something important: a cleaner separation between the top of the «write area» and the bottom of the window header.
Not very simple to explain, so a picture will help:
While the font can have an impact here, the picture shows the same font being used on kate and on BBEdit (monaco 12).
Also, changing fonts just to get some «air» above the first line is not something I would consider. The font has to accommodate my eyes on the whole document and it’s obviously a priority.
For the same reason, increasing the line height factor is effective on the first line but has a negative impact on the rest of the document.