My pet theory is that any time the 'rise' of a quill stem exceeds the 'run', it will look awkward. That's when you switch to a 90 degree stem. On my KHS frame since the top tube was so long I ended up going to a 70mm stem and ran into the rise over run problem:
Before:


After


The other thing I've learned is that french fit really is the best fit:
My most recent build is my frenchest fit to date, and it rides totally fine: