You dont need simulation to determine buoyancy.
You're overthinking and yet under thinking. Your idea seems to display a lack of understanding of the most basic mechanics of buoyancy.
I am a little confused by your logic. Buoyancy is typically calculated as the weight of the fluid displaced by an immersed object. So what you should be looking into is the volume of the object that you are immersing, not the surface area parallel to some plane.