Is a wrap mortgage and subject to the same thing?

[Keith W.]

In my research on the "Subject to" financing technique, some are referring it to a "Wrap-Around Mortgage". 

My understanding of "Subject to" is that we would create an agreement that we would be taking over the payments in exchange for control of the deed, etc.

When looking a the "Wraparound Mortgage", specifically, it looks like there is a spread between what is paid to the seller and his mortgage lender.  

In other words, in a "subject to deal", if the mortgage payment is $1000K per month we pay that amount. On the other hand, for "wrap mortgage" we're paying the $1000K plus an additional amount based on an agreed to purchase price. 

Is this correct, or are these just two various ways it can done?