I did some testing with and without realish tank physx and it's a default l4d thing spinning objects can hit you alot of times a second, e.g. car spinning like crazy hits you collides alot of times persecond, also fixed a bug on my other plugin tank damage modifier after testing props so sorry it's valve
However if my testing is wrong i'm unsure how to approach this.
But gameplay with realish tank physx it's easer to get insta killed by props because your moving while incapped triggering damage.