In the AD8561 datasheet, page 8, a hysteresis circuit is shown:
The capacitor CF is added to introduce a pole into the feedback network.
The calculation for this pole is:
Is this formula correct? In the formula, I would use R1 instead of R2.
I didn't quite get your question, what formula are you pertaining that you mention you'll use R1 and R2?
The formula for your filter is correct, for the hysteresis formula, you can refer to the document below.