Help please for growing Nepeta Walkers Blue

[pfm64]

I have planted Nepeta Walkers Blue as a border/underplanting for my rose beds. I have planted them fairly close together but they seem to be quite flat (leaves and flowers).

Have you any sugestions to help them bush up and flower well? Supposedly they grow 45cm x 45cm.

I have heard mixed reports about cutting them back. Some say cut them back hard each year while others suggest leaving them alone.

I have a magazine photo of a rose garden with this variety of nepeta taken in spring and looking beautiful. Mine are yet to even get close!

Any tips would be rgeatly appreciated!