What exactly are size, ratio and line distance in Eagle PCB text tool?
I'm pretty sure those are attributes that apply to text elements.  Size changes the height of the letters, Ratio changes the thickness of the letters, and distance (I think) affects the vertical space between lines (obviously only for multi-line texts), but context would help to clarify.

As far as vector, proportional, or fixed -- I just always use Vector to avoid surprises when it comes time to generate Gerber files. Seriously, I have no idea why it's not the default. 

A picture is worth a thousand words, as they say. Experiment to see the effect of changing properties and how they interact.