Complex sentence: Setting aside the fact that Bristol was the larger of the two, they were designed to be proportionally identical, thus providing identical relationships between actors on the stage and spectators who surrounded them on three sides, albeit with the great majority to the front.
Split into simpler sentences: Setting aside the fact that Bristol was the larger of the two, their designs are proportionally comparable, if not identical. They provided identical relationships between actors on the stage and spectators "who surrounded them on three sides," albeit with the great majority to the front.