Luck of the draw is perhaps your Betta, I try to keep my Betta fed, found 8 or more pellets and he doesn't eat much the next morning, my ritual is 3 in the morning and 1 to 3 max in evening works great, so far my two Ghost Shrimp made it the first week. Perhaps a fed Betta is best, try to avoid fasting ! Betta will overfeed if you let, likely very reason some fast them. Hungry and Look out Shrimp. Good news Shrimp are only 33 cents.
Meanwhile checking to see if my Shrimp survived another day
My Shrimp on Marimo moss