I knew about the haircut rule, but didn't realize that this was how they had implemented it. I did the calculation in one of my scripts (which is how I first noticed the discrepancy), and it gives back the same answer by a different method (cross multiplication using numbers of token in circulation):

$ ./sbd_ratio.sh
Price: $ 0.2220
STEEM supply: 480295827
SBD supply (cap): 12108259
STEEM Market Cap (calculated): 106625673
SBD supply (cap) / STEEM CAP: 0.1136
SBD print rate: 0 (calculated), 0 (queried)

Lower threshold: 0.2521
Upper threshold: 0.280111

Calculated like this:

echo ${STEEM_SUPPLY} ${SBD_STOP_PERCENT} ${SBD_SUPPLY} | awk '{print "Lower threshold: " 10000 * $3 / ($1 * $2) }'
echo ${STEEM_SUPPLY} ${SBD_START_PERCENT} ${SBD_SUPPLY} | awk '{print "Upper threshold: " 10000 * $3 / ($1 * $2) }'