That particular aspect is only one of the many variables that define a mixed member system. Probably much more important, or just as important, what is no less important than the number of seats you allocate to the proportional theory is how much cross-contamination you allow.
Look at the German system. The German system is known as a mixed member system, but Professor Massicotte's name has come up before, and he went on the record many times to say that it is actually a list PR system in terms of its fundamental outcome, because the proportional peer, the outcome of the party list vote, determines the overall allocation of seats.
Do voters know that? How many voters will know that when they are presented with the choice of voting for a party on the party ballot and for a candidate on the constituency ballot?
There are all kinds of complications. What if the constituency seats that the party gets entitled to actually exceed the number of seats that the party would be entitled to under the proportional vote? You can correct for all of those, but those need to be also checked and looked at. When I—