Baoli: Thanks for the feedback - we may eventually do a % spread filter but our first concern was to do it in $$. After a certain amount of cents you just don't want to see such wide spreads - regardless what the dollar price is of the stock - 1.e., 2% of GOOG. I put a Max spread amount of $0.15 and the tool keeps me away from bad/disadvantaged fills. You can also improve your OddsMaker results by using the Max Distance from Inside Market - which you can express as a percentage.
Baoli: Came up with one possibility: Yhe only other solution, which is quite cumbersome, would be to split your ticker windows into certain price groups and then adjusting the spread accordingly...