Automatically chosen drop rate doesn't look right

When you let Tippecanoe choose a drop rate with `-rg`, it always makes the low zooms look too bright and the high zooms too dark, even though it is equalizing the density of the densest tile at each level. How can it characterize the increased clumpiness of the low zooms and choose better?

Start by investigating the -rg automatic drop-rate path and compare its behavior at low and high zoom levels. The issue provides no file or test entry point; done would mean characterizing increased low-zoom clumpiness and choosing drop rates that avoid the reported brightness imbalance.

Written by the indexing model from the issue text.