That is the shortest explanation you'll get that is still accurate.
Are you looking at the same tooltip as I am? The one I'm looking at certainly quantifies both pull and push.
For an explanation on the mechanics of migration, I'll link to another of my posts
https://forum.paradoxplaza.com/forum/index.php?threads/on-migration.1139824/
That's exactly the tooltip I'm referring to.
As you can see from it, the 1.8% from housing isn't being factored into the headline "Immigration Pull: 115".
Likewise when Free Haven is active, while you'll see a "+50% Free Haven" modifier shown, the headline value
will not change.
Is it working? isn't it? who knows!
Neither the tooltip nor anywhere else in the UI shows the 'effective' value, so we've got no easy way of verifying if it's actually doing anything.
Moreover, even if it is being applied, nowhere is it explained how that pull (or push) rating translates into actual pop migration values.
How much migration gain will you get if, for example, a planet had a pull rating of 1000? or even 10000?
Does it depend upon the pull/push ratings of the other planets to which you have migration access?
Does the number of worlds, and population of said worlds have an impact?
Are there any other factors & modifiers?
As far as I can tell, the entire system is left completely unexplained.
There's simply no way of quantifying how good "+50% migration pull" is without this information*, or indeed if it's even working at all!
*(experimentation should be possible to reverse engineer some of this knowledge.... but that
really shouldn't be necessary)