I think there's even more factors. Southern stream synoptic events always have a fairly deep saturated isothermal layer below the DGZ while clippers have a very thin one. That isothermal layer seems to favor chunkier plates as opposed to spindly dendrites. They just don't form large aggregates the way pure dendrites do. You still get a lot of bigger aggregates mixed in within the heavier bands, but the abundance plates falling at the same time fills in the air gaps and lowers the ratios even so.