Yesterday i had a mortar impact right in front of me - one step closer and it would have been a headshot. I took like 20 damage and wondered what that explosion was. It looked big, but no damage? weird. Took me a bit to notice the Mortar Symbol.
Then, after unlocking it myself, i gave it a test on Sobek. You know, Snipers Paradise. Lots of stationary Targets...one kill. I got one kill.
It destroyed a bunch of Gadgets, which is nice, but thats not its indended use? Enemies, even on a direct hit, took at best 50 damage.
As others have stated, Smoke doesnt work at all.
So...my guess is, that there is a numerical error with the explosion. The current damage radius does not match the visual. And assuming that smoke uses a calculation for its effect, that might be the case.