Yes it does matter. In your scheduler, how do you ensure your ping (the way you start an instance) is actually creating another instance to keep warm or reusing another instance?
If you want to always keep 20 instances warm, you have to keep the first ping active until the 20th one is done.
In other words, if you want to keep 20 active instances warm and you send 20 requests in 5 seconds, if each request only takes .25 seconds. You will only have 5 warm lambdas. The 6th real concurrent connection will still have a cold start. Also while you are pinging the request to keep it warm, that instance can serve a real user.
Also, API Gateway has an algorithm to decide whether to launch a new lambda are cache a request hoping that using an already warm lambda will free up.
