Passing regardingobjectidtype to Xrm.Utility.openEntityForm

I've been having troubles sending the typename to the openEntity form. Is this a problem with my system or is there another way I should be setting the typename?

Here is the code I am trying to use.

//set the parameters to pass to the new form
var Regarding = Xrm.Page.getAttribute("regardingobjectid").getValue();
var parameters = {};
parameters["regardingobjectid"] = Regarding[0].id;
parameters["regardingobjectidname"] = Regarding[0].name;
parameters["regardingobjectidtype"] = Regarding[0].typename;

//Open the new form
Xrm.Utility.openEntityForm("appointment",null,parameters);

I've been able to send owneridtype and customeridtype without a problem, but regardingobjecttype does not seem to be working for me.

Thanks!