Interesting and good to know they stack. For those interested the following will plot the combined damage function in wolfram alpha (at half flux for EWM):
Plot[Piecewise[{{25, x < 600}, {25*(2.5-x/400), 800 > x > 600},{25*(2.5-x/400)+30*(x/800-1), 1000 > x > 800},{30*(x/800-1), 1600 > x > 100}}], {x, 0, 1600}]