chain adjustment question

my chain slack done by the book is still within spec at 30mm, but I realised yesterday that whereas I thought I was pushing the chain upwards until its own tension stopped it, that's not the case, and the upper limit is dictated by it hitting some kind of plastic guide on the underside of the swingarm. So I made sure the top side of the chain was tight (I think I rolled the bike backwards slightly), and this caused the bottom of the chain to sag further, meaning this time when I checked the travel it was 40mm.
So what's the right way of doing it - top of chain tight, or relaxed?
Mike

The top of the chain should be 'tight,' but regardless whether it starts this way or not, once you pull/push all the slack out of the bottom side of the chain the countershaft sprocket will rotate and thus any top-side slack will be elimminated.

...Unless you have the bike in gear...