Poor LED dimming performance
Problem (mostly) solved.  It turns out most dimmers have a way to adjust the minimum level of the dimmer.  The way to adjust my dimmer was very unintuitive, but it allowed me to crank it down to about 10%, where it shipped with a minimum brightness of about 50% 

Lutron has a nice video on their dimmer site that shows how to make the adjustment.  Other brands of dimmers have different ways of adjusting the minimum output.