In the south full sun is a challenging site for azaleas. You can probably get by with it if you keep the soil adequately moist. Azaleas in general love a bright shade with some dappled or morning sun. As the shade gets darker (less light intensity) they will grow but not bloom as well. It is difficult to judge you shade by an online description but I don't think I would mix types. If you like the Encore description go with those for the entire row. However Monrovia carries quite a few that are well adapted to a lot of sun. I think 'Nuccio's Wild Cherry' would be a good choice as would Higasa or any of the azaleas with smaller foliage. Check out those on Monrovia's web site and click on Growth Conditions for more detail on whether a particular variety takes full sun or not.
It may be that in time you will decide to trim up the trees a bit to brighten the shade to improve any varieties performance if the shade is just too dense.
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