7a isn't so bad, we hardly dip below 10 degrees. A lot of plants that were formerly thought not hardy here are proving hardy the last few years. I have some cape fuchsia pulling through. Yes, 'Goshiki' osmanthus is fully hardy here and I planted quite a few at my cousins. They can get massive I saw a mature specimen at a nursery near her house. I worry it will not fill the space as they are very slow growing though and more rotund than tall. I have seen a few other osmanthus at nurseries but they aren't offered here too much due to our area having variable dips in zones, it's super erratic so many places don't carry certain things and its only in the last few years that more solid zone 7 plants have been showing up in MD at nurseries. Our yard is definitely zone 7a though.

Tricia, Rhododendrum is evergreen and might do well in that spot if there is no afternoon sun. You can prune it if it gets too big and it will have nice flowers in Spring. Mountain Laurel, the PA state shrub is evergreen and has flowers, won't get real high for you. Variegated privet is really beautiful and you could shape it any way you like, takes abuse and flowers in spring. All green, there are boxwoods, you could shape nice, even a topiary which would look different. Some azelas might do alright there, there are evergreen ones, if you mulch them real good. Encore azelas might make it in your zone well mulched and bloom off and on through the summer. If you go with a rhodo, amend the soil real good with spagnum peat moss and mabey a few rocks, since your soil is clayish. Chuck Hayes gardenia is evergreen, and if you amend the soil like a rhodo, you could have a beautiful gardenia out front and boy do they boom in the spring and the whole neighborhood smells it. There were people on this forum from Philadelphia that had a 4 foot Chuck Hayes that grew well, they had to trim some of it down.(check Fragrant forum, input Chuck Hayes). SOrry, ran out of ideas. Hope you find something nice.

Try a Galvezia: tough as nails, drought tolerant, bright red snapdragon blooms beloved of hummers. These are the best: 'Boca Rosa' - forms a dense mound with arching stems reaching to 4 feet tall. In the summer through early fall it produces tubular bright red flowers which are flared at the lip, resembling small snapdragon flowers. Plant in full sun to moderate shade in well-drained soil. It is drought tolerant, especially if planted in shade. foliage is a larval food source for our local Checkerspot butterfly. Prune occasionally for denser growth 'Firecracker' is more compact.

"Tiny Towers" Italian Cypress are superb for tall and narrow. They don't get gigantic like the big ones do. Spearmint Juniper is also great. Beautiful green color and takes to shearing very easily. "Purple Pony" purple leaf plum is also excellent as a small tree. Only gets about 12' tall. Doesn't get huge like the big ones do... There are also some smaller Cassias that do well as small trees and have nice flowers as well and are only briefly deciduous.