The plot behavior looks correct to me, according to the equation.
If delta_V == 0, then lambda == 1. (You don't calculate/plot this point, but that is the result you get.)
In the limit that delta_V gets large, lambda gets smaller, and goes to
ks_1 = 0.1;
-ks_1 / (1 - ks_1) % when N == 1
This seems to be what your plot does. So, I don't see a problem. But maybe I am not understanding something.