AWS subnets for lambda synchronous invocations

Am I right in thinking giving a lambda using an API gateway 3 subnets each with a range of 16 would result in 2 subnets being used at once and 1 IP used for the API gateway that is in the same subnets resulting in a max of 31 invocations before the error code 429 is returned due to Too Many Requests.This is my thinking as there should be no other resources using an ip address that will be in these subnets but I can see testing it as being complicated and taking a very significant amount of time with my current knowledge.