It is not advisable to have seating/benching too close to the ceiling as heat rises so the temperature will be higher than what you have set on your control.
Basic steam room construction guidelines do not recommend ceiling heights to be above 8 feet and seat heights should be 18-21 inches. This doesn't leave much room for an additional tier of benching.
Without knowing the specifics of your environment, I would suggest you speak with a Bathing Environment Specialist
to review your preferences and determine the best way to achieve them.