Sometimes the form does matter. Is it more like a ball or shaped like a stick? It channels the energy differentially. Also I think size matters, but not in the scale we experience. In my opinion a smaller stone needs recharging or cleaning more often (if it's used as a storage stone, this will not be the case for a stone used for transformation or a stone that channels just the energy), but the timescale will be maybe one year to 10 years. Normally you will clean or recharge more often. Also, this is only my personal feeling, there may be different approaches to stones.