domain mapping with ip 123.123.123.123/~sitename

So, heres a fun one..
If i go to my ip address in a browser, I get the 'good job cpanel is installed page' I contacted support and they told me that to view the page i would need to go to http://my.ip.1.234/~accountname/
would i need to contact my support and make sure that the mu install loads when i go to http://myip ?

should I register a custom nameserver to http://my.ip.1.234/~accountname/
and point the A record at the nameserver instead?

I've set the A record to just my ip and am waiting to see if it works. but i have a bad feeling that as my site wont load at just http://myip , then domain mapping wont find the install..