Maybe what are locally called “ghost shrimp” in your area is different. A lot of different species are often sold as ghost shrimp but the Paleomonetes species ghost shrimp which is what most of them are, are the same adult size as an amano 1.5-2 inches.
I think the point of this conversation for the OP is, they might get eaten so if you’re going to try shrimp start out with just a couple and larger shrimp, if you can, to see if your betta will leave them alone.