dude not every voltorb is exactly 2 feet
there are small and big Pokémon
https://bulbapedia.bulbagarden.net/wiki/Personality_value#Size> The final value of Size is bounded between 0.29 and 1.725 times the standard height given for the species in the Pokédex, and rounded down.>.29So they actually can be a bit under 3 times as small as the average.
adding onto this, voltorbs are on average 20 inches in size, and to find one 3 times smaller would be about 6.5 inches in size. Which is only a bit bigger relatively than a pokeball diamater.
plus pokemon can change size too
