i presume detmer you mean something that changes turns gained walling from

8 attacks and 18.666 turns wasted for every 1 turn walling at 5 civ/gs and something like .7 attacks per turn walling at near max pop

if you put it over 1 at near max pop and decreased it to under 1 at low pop that encourages people to wall gradually and makes it so with enough persistence about 2-3 people could eventually get a kill

ive seen people talking about low-high-low percentage kills rather than flat or low-high though