Thanks for the response.
I think you are right - ie, oils have more control.
I gave it a try with my most recent project. (Dot filters only applied to the turret in these shots).
These are the before filter shots:
Post dot filters - i used MM enamels. It doesn't show as well in the photos, but under my own eyes i can see very faint lines/dot filter effect. Overall, however, i was happy with the sublte way they tied together the overall scheme and softened it a bit.
I think in hindsight, maybe dot filtering works better if you use oils, as you have a bit more time to play with the colours etc before they dry. I found the MM enamels tended to dry a little too fast.
Also, i think the effect with oils would work better with mono paint schemes - perhaps with a mottled scheme it's harder to recognise?