I expect that you haven't had much help because of the extremely small height of the hedge! Have you considered something like Liriope?

maybe 'gumpo' azaleas? might ultimately exceed 18" but can be shaped and is not a real fast grower.
they come in pink, red and white flowered forms and bloom here in may/june so would appreciate some shade at that time of year.
they have a low, spreading habit and are evergreen.

Here is a link that might be useful: azalea 'gumpo'

Upright germander (teucrium chamaedrys.) Evergreen, stays small, very tidy full mounds, takes well to shearing. You can either plant it a bit farther apart, let it mound and bloom, or you can plant it really close together and keep it sheared. Looks good either way, takes sun or part shade. An old plant that for some reason isn't used as much anymore....it was used for tidy little borders for herb and knot gardens.

For a very classic look, I use true dwarf boxwoods, buxus sempervirens 'suffruticosa'. Make sure you get this exact variety since some tags say 'dwarf boxwoods' but aren't the same. Very neat, nice green foliage, takes part sun/part shade. It must have good drainage. Amend the soil. It also will not require a lot of water. You can purchase 1 gal. size which are about 12" tall and can be maintained to the height you want. Get your color from the other plants you plant.

I saw the cutest hedge on a garden tour. Small Italian cypresses planted about 2 ft apart then the tops were split down the middle,bent over and wired to it's neighbor at the top to form little arches. I don't know if that makes sense, but it was adorable around a small flower bed.

Ilex vomitoria 'Stokes Dwarf'

A neat little hedge that stopped me in my tracks when I realized what it was - was MINT! Even tasted it to be sure. I don't think it would be considered an evergreen in Philadelphia where I saw it, but it might be further south. I live in FL and the stuff is downright invasive here! It only took one season for me to learn to pot all mints. cora

Sarcococca, Himalayan sweet box (not to be confused with Himalayan boxwood), likes partial shade and doesn't get above 18 inches tall. It's a good spreader, so should fill in to make a nice hedge in just a few years.

Yes, Stokes Dwarf is great and they tolerate different soil conditions. They also grow nicely into each other and are a quick trim on the top.
Ilex vomitoria Stokes Dwarf/dwarf yaupon holly. And, if deer are a problem in your area dwarf yaupon are not one of their preferred foods.

Have you considered a cotoneaster. There are a few varieties that can be maintained as a small hedge. James