Crossbloom 1.0.1 is live with the fix you suggested. The cross on the grass now scores the share of a tree's bloom days that have a partner. An early tree beside a mid tree now shows amber instead of green, and the info line says about 40 percent of a crop and why. Partial partners draw dashed lines when you hover a tree.
We fixed one related case too. A tree planted in spring is now judged against the partners of next spring, because that is when it first blooms.
Thanks again for reading the source so closely.