You really need to look at a real measurement system. Getting proper crossovers is not easy (you have no idea of any kind of "time") with an RTA.
Getting the time right (and remember that there is a different time "delay" with each of the different low pass filters-so they have to be adjusted (via delay) in order to get them to "line up") is practically impossible.
It may "look" like it is right-but is not actually right.
I am working on a little paper that shows how a measurement system can "look right", but in reality it is wrong. Depending on how it is setup. And RTA is the worst case (or best case-depending on the perspective) in not "telling the truth".