Really liked this investigation - maths, physics, data and enthusiasm all together!

I see the physics model you used assumes a constant rotation and from this comes a non-exponential physics-based law - completely agree there is not enough data to tell which applies. But in fact an exponential component could enter the physics from the unstable gyroscopic motion of the tube of polish as it spins in the air. In rotational motion, a slightly distorted cylinder has two attractive stationary axes and one repulsive. If the tube's rotation axis happened to start close to one of these stationary axes, it would precess approximately exponentially towards or away, at least for the short time in the air.

So the exponential guess by eye may be the right physics as well but, with more degrees of freedom, this would need even more data to confirm it. And more mess to clean up.