I think this is an excellent idea, though it depends upon your magic being loose enough to accept this. Some fictional (aren't they all) examples of circle use are so exacting as having a hair drop across a line is sufficient to blow the protection. With such standards, a carpet would be play Russian roulette with 5 rounds loaded.
For D&D though, or lower-stakes magic, I see this as perfectly fitting. Go to Comment
If it was a castle, it was the strangest one he had ever seen.
He of course saw the main tower - taller than anything he had seen outside of Stoneholt, the spire looked fragile and was topped by a glassed-in chamber.
The outer wall was so gently sloped that it would have only stopped a horde of hobbling old men, an able-bodied soldier could stride up to its crest with little effort. Within one saw a huge, nearly perfect bowl-shaped area with the base of the tower in the centre, covered in hundreds of mirrors.
This structure is a massive solar collector designed by the Wizard-King Aardwal in centuries past. He used the concentrated light in his investigations into the magic of light, and in the fashioning of flash crystals.