First of all, the “default” match detection option is something that you choose under Settings > Auto-Fill . Default URI Match Detection. When you first set up a Bitwarden browser extension, the default method is “Base Domain”, but this can be changed if something else fits your needs better.
Second, the most straightforward way to solve your problem, as I suggested above, is to define your three vault items as follows:
cPanel Item:
URI 1: https://iamdannywyatt.com/cpanel (Match Detection: Host)
URI 2: https://iamdannywyatt.com:2083 (Match Detection: Host)
Forum Item:
URI 1: https://forum.iamdannywyatt.com/ (Match Detection: Host)
Port 2096 Item:
URI 1: https://iamdannywyatt.com:2096 (Match Detection: Host)
Regex is also possible, but it is more difficult to set up and maintain, and opens the possibility for creating a security vulenrability.
It excludes the URI from being considered in the match detection algorithm (as if the URI was never there to begin with). I was describing the way that option works in Bitwarden, which may or may not make sense to you. Some people use it as a way of archiving unused items (to prevent those items from being matched); another use-case is if you want URI 1 to be used as the URL to be launched, or be used as a source for the displayed favicon, but you only want your credentials auto-filled on URLs that match URI 2, etc.
If you would like for the “Never” option to work in a different way, you might consider voting for the following feature request (or submitting your own):