Grid changes on zoom

I know I used to have Reaper set up so that as I zoomed in the grid would get more detailed. By that I mean that the grid lines always looked about the same, but as you zoomed in you'd obviously be getting finer divisions. I hope that's clear ?! But somehow I seemed to have lost that and just can't see where I reactivate it. Anyone remind me ?

Right-click the Snap tool on the main toolbar andcheck your setting there?

Yes ! About halfway down 'grid snap spacing'. Thanks :-)