Tf2 - Ullapool Caber Has Damage Fall off?? 

The way the blast works is: the closer you are to the explosion the more damage it does, so technically yes it has slight damage fall off, this also means crouching and hitting a player's feet will do more damage than if you hit them at their head.

when you are further away less of the explosion hit box hits the enemy doing less damage

no wayyy, that's why caber now feels so janky

This explains the random damage some times 1 shoting a medic and other times not killing a sniper