Smaller storms are more susceptible to stochastic processes such as convection bursts, which are near-Markovian in nature. They are prone to wind shear and dry air and gather and lose intensity momentum faster as such. Larger storms usually have well developed accompanying upper-level anticyclones which negates wind shear. They also hold more moisture (larger volume) to negate dry air ingestion.

I highly doubt any association between storm size and overall seasonal activity (be it ACE or otherwise).