Miniature size and shading

[Conquistador]

I have two flavors of Army Painter Quickshade.

Soft and Dark (budget limits keeping it to two) and I have been experience eating with 25mm+ figures.

Now I am looking at 15mm/18mm figures and I wonder if there is a rule of thumb that suggests using a lighter shading tone for smaller figures? 

[Vermis]

Going by what I've seen of 10mm minis...

http://www.forum.specialist-arms.com/index.php?topic=4426.msg32970#msg32970

... I'd go for dark. Overall I think smaller-scale minis benefit from a little extra contrast.