No experience with Yaupon Holly, but a couple of thoughts. I see a tradeoff between having enough foliage to drive new root growth and having so much foliage that roots struggle to provide water. You imply that the roots may be a bit limited and the picture shows a large shrub in a very nice looking, but not particularly large container. I am thinking that reducing the foliage by about 1/3 might be a good approach. Take out the branches that are particularly long with foliage only at the tips. That will both reduce the water demand upon the roots and provide some interior light to start the back budding process.
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