Thanks for the reply.
Well, I did exactly that the first time over, but now that you mention it, I remember I ran and set them up as they were being installed one by one from the Software Centre, and some of them closed abruptly when the following one started installing. That must have messed up some core installation file that's common to all apps.
I'm reinstalling all and leaving them alone until they're all downloaded and installed, and see if that solves the problem.
EDIT: So this is what's happened after reinstalling everything. I ran and set up all the apps again. It worked fine for all of them except four: Mini, Modular, CS-80 and Synclavier, that were still opening at 90% window size no matter what.
Then, went through each as VSTs from Cubase and I don't think it's a coincidence that those same four were the only ones that showed me the tutorial prompt again. And now everything seems fine for all apps in both standalone and VST.
So I'm still not too sure what's happened, but I'll keep my fingers crossed...