For your temps, I noticed that my cherry shrimps bred much more at lower temps below 77 degrees. I have them at 74 currently.
Some say RCS breed better at warmer temperatures 25-27C, like this article in wikihow
. The majority of sites state this fact.
And shrimp farm
states to keep at the temp and the PH anywhere but the extremes, which to me makes sense that RCS would breed better at an average of the range.
There was a site which I can't seem to find, which stated that the optimium temp is 74-75F.
At the end I've decided to go with the large number of srticles that state 25-27C is the best breeding temp. My only problem is that my fluval 100W heater wont get to that temp. It reaches 24.5C and stays at that value.