# Sample size for proportions and fisher exact test

I need some clarification. I am doing a chart review. Plan to test significance with fisher exact as its two interventions, one yes/no outcome. Presumed prevalence in the population is 15%, but includes both interventions, restrictive and liberal. Would like to see that restrictive has about 10% and liberal stay around 15% for clinical significance which is a 30% reduction. Closest approximation to the restrictive in literature is 9%. I did one test for proportions to calculate sample using a known proportion p0 (9%) and 15% p1 for the other. Which gave me a reasonable number of 207. I plugged that in to a confidence interval calculater too and much the same answer. However i then tried using two proportions of 15 vs 9 in a calculator assuming it is not a known proportion and it gave me a sample of 460 for each group. Where am I going wrong?