At lower per capita volumes, the ratio of fixed to variable cost increases and the cost elasticities decrease (because a greater proportion of total costs is fixed).
At lower per capita volumes, a lesser proportion of total costs is fixed. 
mnli hypothesis: At lower per capita volumes, a lesser proportion of total costs is fixed.  premise: At lower per capita volumes, the ratio of fixed to variable cost increases and the cost elasticities decrease (because a greater proportion of total costs is fixed).