After looking at the feat for a bit more, I noticed that right before the frame of impact on the bottom of the screen, Detainer's claw can be seen, thus this can be used to extend the point at which he was before the impact, increasing his speed and, by that, k.e.
G-Man's head's height - 22,4583333m
Detainer's weight - 18,827,300.2kg
Calc step by step, took the balanced place where Detainer is by his claw's location:
8.2959 Kilotons (Town level) Solid.