You are correct sir!
I've got three of them and have been doing it for over a decade.
I've found in actual practice that the different size EUs play well together and the smaller one contributes without overloading as you might worry it would.
Since we've buried the earlier post a little I'll say again, plug two (or more) EUs together FIRST, THEN start either or both at any time as you wish. Just don't connect them while they are already running.
And all you have to do is cut the female end of an extension cord off, install a male plug, then plug one set into the other.
And of course do not leave one end of such a cord unplugged and touch the exposed prongs - but if that's not obvious, you should just light your camp with a jar full of lightning bugs.
Too much is not enough, and when in doubt double it.