Feeding ratio for starters

I've had a heck of a time getting a really sour sourdough, and I'm convinced that it's my local microflora. I've taken some measures to get more tang out of my bread -- firm starter at 50%, long cool rise, overnight retarding. It helps. But it's only mildly sour, not the sharp tang I'd like to get.

My friend, who lives 4 miles away, took some of my starter. Over the last four weeks, her bread has progressively gotten more sour, and she's doing everything exactly as I do.

Anyway, I'm curious about the ratio of refreshment. I've decided to see what a really liquid starter (125% hydration) like Jeffrey Hammelman uses would do. Now, in the King Arthur Baker's Companion and the BBA, they recommend not going any further than quadrupling when you refresh the starter. Hammelman, on the other hand, increases his by a factor of 8.

I'm trying it out tomorrow, but I'm curious how other folks refresh their starter. Has the ratio had an effect on flavor?