Just went out to Mount Zhayolm today as 72 BST and noticed some of the slimes checked DC. This puts the lower level ones at 71 at most. More testing may be needed, but for now I'm putting the low end spawn range at 71. For reference, the DCs I found were near the eastern most zone to Halvung in the tunnel to the south beach, just in case different areas of the zone have their own level ranges for the clots.
Failed charm multiple times even with CHR+32 and Apollo's Staff as 74 BST.