I can't tell varieties at this distance, but the second group of 2 are certainly smaller, both in height and in diameter of the crown.

It's possible they were a year apart in age when you planted them.

It's possible their conditions are different; soil, water, sun exposure, etc..

It also looks like you lost the one in the middle.

I'd give them more time.

There's a lot to be said for growing grasses to maturity in nursery beds, before creating so formal a display. This way you're more certain you have matching copies.

thanks donn! there isn't one planted in the middle. (sprinkler head there).

we will give them more time. as you can see from last year, they did have the same height. hopefully the little ones will catch up later this summer.

thanks again.

Ah. It looks like there are 5 grasses in last year's pic, and 4 in this year's.