I highly suspect your pH is well too high for the bbs, and will eventually do them in. While I believe both of those potting mixes are peat based, they will be amended to bring the pH up to the range that most plants prefer - too high for bbs.

Some experienced growers advocate afternoon sun for newly planted bbs even if the pH is correct. But, with a high pH that could be interfering with root growth, I would think that full sun on the south side of a house could quickly cook them, no matter how often you water or moisture retentive the mix is. They just won't have the roots to survive in such a situation. I didn't really plan on giving my newly planting bbs afternoon shade, but where I set them up, they do. And they are growing very well this first year.

If you want to save them, I'd highly suggest replanting them in a proper pH mix (pine bark and/or peat), and move them where they will be shaded in the heat of the afternoon.

Kind of what I was thinking. Thanks for the advice. Looks like I'm stopping by Lowes on the way home today.