I like your diagram.
Are you in Ontario, Canada? If so, purple fountain grass will not survive your winter.
The maiden grass, miscanthus, will get the largest. 5 foot circle for it, could get 5 feet tall. Switch grass, maybe a 3 foot circle, might go 4 feet tall. The fescue is small, and stays that way. Only need a 1 foot circle, maybe 1 foot tall.
You want all your grasses together? Me, I think the neatest thing about grasses is the contrasts they make with other unrelated plants. So I mix grasses with perennials and annuals and shrubs and roses and conifers. That's not to say you must do as I do. It's just an idea for your consideration.
Get thee to a library or good bookstore. Find some books on ornamental grasses. Check the sections on designing with grasses. You will see some neat pictures. Copy those designs if you like them.
And beware of buying too many grasses, for they are easy to divide. You can buy one grass, and if it has a good large base, you can just chop it into fourths and you will then have 4 plants that will fill in rather quickly.
Seeing that your plantings are only a few months old, it should be no trouble to move them now. Do a little research and then get busy.

As deep__roots stated grass bed design is entirely up to the gardener.

I have beds that need to be spread out as the grasses are so close that you can not walk through or between them without getting scratched or cut from the fronds or blades.

This isn't a bad thing but yet I have a bed that is more spaced and that does look more orderly and clean and you can have a better look at that various or different grasses growing in those beds.

I even have grasses growing in the middle of no where or as specimens and these look good in that garden scheme.

As for moving the grasses either do it now (others will frown upon this statement) or you will be kicking yourself when you "have" to do next year.

My grasses have exceeded what I thought would be their "full grown" spread and that is how I ended up with the over crowded bed. It might have helped if I would have split them last year or this year but "more important" things took precedence. Yah, Right!!

Just more experiences, successes and failures from another grass grower.

Jake