Each Viball size has the most intense rotational energy, i.e. the maximum vibration strength that can be achieved in this size - more is not physically possible. In addition, the stainless steel of Viball love balls has significantly better vibration and resonance properties compared to silicone products. But differences in the intensity of the different sizes are due to physical reasons: smaller balls naturally have a smaller inner ball with less weight, and therefore less rotational energy than larger ones. The efficiency increases from size to size not only linearly (evenly), but exponentially (increasing more and more), because on the one hand the weight of the respective inner ball increases and at the same time the interior offers proportionally more space for oscillation.
Two smaller balls (VB36-2 or VB40-2) usually have considerably more surface area than the next larger one, thus distributing the vibration over a larger body surface.
This means that although the pair of VB36-2 acts on a larger area than a single 40 mm Viball, it does not achieve the overall impulse strength (vibration intensity) per area.