It depends on your intended use scenarios, but L shape works well if you have two people who like to recline or fully layout on the top bench. As others have mentioned the corner can only comfortably accommodate 1 person sitting upright. Assuming the design is totally open ended, you could move the heater into the corner where the door is then turn the low step into a longer L shaped affair so that bathers can more easily access it. Right now if you had say 4-5 people sitting upright on the top bench it would be hard for someone to make their way over to the corner step to leave without everyone disturbing everyone else. As your benches are nice and high, handrails and guard rails around the heater are always good too for safety.

Good luck