Eye in the belly
A potential eye, such as this one at the marked point, may have a big effect on the almost filling of groups. It doesn't need to be a real eye to make a difference.
Note on polite English: 'belly' might be considered a little colloquial, or childish, compared with 'stomach', in spoken English. There is a further example (in the centre) at the end of killable eye shapes called 'eye in the stomach'.
jsha: However, 'belly' has some appropriate connotations. The belly is traditionally one of the most vulnerable parts of a dragon, and as such is a good place to strike. Also, something is said to 'go belly up' when it dies. iopq: Also, belly sometimes means "middle" as in the expression "right in the belly." I believe it's a better term.