I found that using the shockwave ability with enemies on rooftops will snag you the "High Fall" bonus a majority of the time.
Just go up high in an area you have no liberated, find people on the roof and send them flying with the shockwave (L1 + X). It is easier if you do this with Reapers in the Neon District, as they are the weakest of the enemies. This will work most of the time on Dust Men too in the Warrens, but I had a much harder time with the First Sons in the Historic District. Most of the time they would fall, but would die
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