I don't know what my top tube length is, but when I got my Luna, it turned out to be smaller than any bike I've ever ridden. I'm 5'6" and it's about a 49cm (custom, so not exact). It's also the MOST comfortable bike I've ever ridden.

Sounds like you got a sweet fit. Don't overthink it if it works. Just ride and have fun. Congratulations on your new bike!