Multisite Domain Mapping Woes (VPS)

Alright, here's my question. I have several websites set up with Worthwhile hosting based out of Greenville, SC. I decided to start simplifying my plugin updates by switching them over to a multisite under our main site (minutemenministries.org) one by one (with a ground up redesign for each one, too).

So I switched over the first over Christmas (jimvangelderen.org). I got the site up, designed, and prettified and then set out to map the old domain to the new site (minutemenministries.org/jimvangelderem/) using the wordpress domain mapping plugin out there. I followed the steps from tutorials I've seen out there and was able to get everything going except for the IP. The IP for both sites was the same, and thus the host records for both domains were the same as well, but typing those domains into a browser returned different sites that reflected the different folders in my ftp.

I did some investigation (knowing nothing previously about how any of this worked) and concluded that my host must be using some kind of a VPS to diagnose which FTP folder to point to. I asked me host to switch the VPS record to point jimvangelderen.org to minutemenministries.org, hoping that I could then switch my primary domain for the subsite to jimvangelderen.org and the plugin would take care of the rest... No dice.

Once the changes were reflected and jimvangelderen.org returned minutemenministries.org when I typed it into a browser, I changed the primary domain for my /jimvangelderen subsite to jimvangelderen.org. Immediately, it logged me out, said I didn't have permissions to access the page, and jimvangelderen.org still redirected me to minutemenministries.org, not to the subsite.

I was able to reverse the changes in my network settings, but I am at a loss of where to go next. I am sorry if I am not saying things right, but I am new to the concept of VPS, and my host has total control over its records. Any thoughts?