Anonymous Access Requirements - Custom FBA Login Form

Good Day,

Is there a way to deploy a custom FBA login form so that one doesn't need to enable anonymous access on the web application in order for users to see this login form anonymously?

My solution currently deploys to /layouts/15/My.SSO/login.aspx, and I've correctly set the URL in the web applications Custom Sign In Page field. However, when navigating to the site, I am prompted for NTLM credentials before hitting the form. The default FBA login form does not require authentication, and I'd like to replicate that behavior.

Thanks,

Chris