I ended up having to open a support ticket about this. In the end we came up with a workaround to resolve the problem and I have included this below:
"Colin, engineering says the system is working as designed since external calls are supposed to have a distinctive ring. I wrote up a header manipulation script that will strip the alert from the INVITE and not override the phone config. Please add this from the global config prompt:"
hmr policy CustomRing
rule-set CustomRing 5
hmr rule-set CustomRing
message-rule StripAlert message-type request 5
remove header alert-info position first match-value Bellcore-dr2 5
sip hmr CustomRing out