I don't think it is the elevation, per se, I think it is the cold that accompanies the elevation. Hence, 300' elevation in a warmer zone is different than 300' elevation in a colder zone.

R. cumberlandense, the Cumberland Azalea, is a low deciduous azalea found in Kentucky, Virginia, Tennessee, North Carolina, Georgia and Alabama. It has long been grown under the name, R. bakeri. It is an excellent, low-growing, late blooming orange to red-flowered azalea suitable for small gardens. The flowers are not large, about 1.5 to 1.75 inches across, and typically range from yellowish-orange to deep red. This species is sometimes difficult to distinguish from the larger flowered R. calendulaceum , but the blossoms generally appear several weeks later after the leaves have fully expanded and the undersides of the leaves are usually waxy white or bluish in color. The species distinction for R. cumberlandense was first described by Lemon and McKay in 1937. This native azalea makes an excellent landscape plant in its own right, but it also hybridizes easily with many of the other species, producing beautiful hybrids in a broad range of colors. R. indicum, or the Satsuki azalea, is one of the oldest evergreen Japanese azaleas, bred since ancient times, and it is the type most commonly used for ornamental pruning. It is a slow-growing evergreen shrub that eventually becomes 3 to 6 feet tall and is hardy to Zone 5, to -15° F. Its 1 1/2-inch-long oval leaves grow on finely twigged branches. In the species, the flowers are red tinged with purple, about 2 to 3 inches wide, but it has been bred in many other colors.

R. vaseyi, the Pink Shell Azalea, is a medium to tall deciduous azalea found in North and South Carolina. It does very well in cultivation, especially in moist soils. It has showy dark pink flowers. It also has a white variation. It has showy fall foliage when the willow-like leaves turn yellow and red. Discovered by George Vasey in 1878, this native azalea has a relatively restricted natural habitat in four mountainous counties of North Carolina. Growing at elevations of 3000 to 5500 feet, the rare Pinkshell azalea can be seen in bloom along the Blue Ridge Parkway in early spring. Delicate R. vaseyi, pinkshell azalea, grow best in the moist soil bordering ponds in Zones 5-8, hardy to -10° F, where they grow 6 to 8 feet tall and bears 1 1/2-inch pink flowers in late spring to early summer.

Thanks Rhodyman, typically our low temperature would be in the teens and that only happens a few times per year and not more than a couple of days of longevity. I had spoken with a grower in Georgia that is at about 600' elevation and these 2 azaleas struggle there. He inferred it may have something to do with elevation.
I was curious if anyone had any luck with them at lower elevations.