What design aspect of a tube feeder should be scrutinized to prevent larger finches or chickadees from dominating it?

The distance between feeding ports/perches.

When evaluating tube feeders intended for goldfinches, paying close attention to the spacing between the individual feeding ports is critical for managing bird hierarchy at the feeder. If the perches are spaced too widely apart, larger, more aggressive species, such as certain finches or chickadees, might take up multiple feeding stations simultaneously. This over-occupancy can effectively chase away the smaller target species, the American Goldfinches, leading to inconsistent visitation. A well-designed feeder balances the number of available ports with ensuring sufficient physical space for the target species to feed comfortably without overcrowding.