The total amount of SP delegation is 14K, of which 14K is the bots. 80% of this is given to the delegators. Effectively improving your ROI by 1400 * 0.8 / 12600 = 8.9 % improvement.
The money received today is 0.64 / 14000. The annualised rate is (1 + 0.64 / 14000 * 1.08) ^ 365 = 1.8%, without it, it is 1.6%. Take off the 10% transferred daily, gives 1.44%.
I can check the calculculation for accuracy, but that is the general idea.
Returns are quoted in SBD. Similarly, 9% SBD return converted to STEEM return is 9% * 2.5 roughly or 23.5 %