Probably cause of the fact that the trasurer wishes to fix the max rate at 6.6% 94000=6% phobos premium=0.5% put premium=.168% that would give a total of 6.668% the other two options give you an max interest rate of 6.795% & 6.55%,but in the latter case the premium is high and it would be a waste if the interest rate happens to fall,so we stick the cap at 94000.