We're in the process of designing our pool and patio for next spring and having a fire pit with seating wall put in. What's a good height for the fire pit? The patio guy said they usually do 15" finished height, but I asked to bring it up to 18". The seating wall finished height will be 21". Fire pit will be 4.5' round. Seating wall will be 3' from the fire pit. They originally had 4', but I said that's too far and moved it closer to the 3' mark.