Lizzy, I don't see a wide range of information on this newer hybrid. Those few descriptions I do find say heat tolerant, which may not be the same as sun tolerant. The page you link has conflicting information - It shows Exposure: Shade to Part Sun, then contradicts itself under characteristics as suggesting full sun to part shade.

It sounds as though your mid afternoon sun site is going to be too bright if this is your second rhododendron planting there without plants thriving.

Almost any plant that is moved from a shady location to a sunny location will get sun burn. You also see this when you prune rhododendrons. The newly exposed leaves will sunburn.

Usually plants die from poor cultural conditions. The main requirements are drainage, adequate moisture (no more), acidic soil, a good mulch to keep the roots cool, and partial shade.

Rhododendrons planed too deeply in clay soil without opening up the roots and soaking the root ball before planting will die a most certain death whether you have sun or shade.

Here is a link that might be useful: How to care for rhododendrons