How to optimize the distribution of load created by Locust

I am load testing a web application using locustio. I am using locust in distributed mode and hitting 5 AWS instances with 5 slaves. I notice that the load created from each slave hits only a specific web server of the 5 AWS web servers.

1. I guess it has to do with the IP that the load comes from.. Does it?

2. Would it be a good approach to setup , let's say 50 slaves, so the distribution would be more even? I want to check that the Amazon Load Balancer kicks in and does a good job sending new requests to idle instances when the CPU load increases.