I agree with Gloria.
Delving deeper, in the selection of medium - size, type, etc. - the size of the roots is only a single consideration out of many.
First, think about what the medium is supposed to do:
- Provide mechanical stability for the plant
- Retain moisture and nutrition
- Allow plenty of air flow to the roots
- Retain those properties for as long a period of time as possible
Then think about the specific properties of the materials you can choose from as they relate to those parameters, and how your growing conditions and personal fastidiousness may interact with them - if you want to "mess with" your plants a lot and water frequently, choose a medium that dries out rapidly, but be aware that drier conditions already favor that.
It's a giant "juggling" exercise involving lots of parameters - light level, humidity, air movement, and temperature - not to mention the needs of the plant, and will become more obvious as you pay attention and get more experience.
By the way, I would consider your 1/4"-1/2" grade to be more medium than fine.