I think there is an issue with the sensor bomb, it always staggers Tanks regardless of what the l4d2_flare_gun_hurt_stumble cvar is set to. I also tried installing "
Stumble - Grenade Launcher" and set its cvar l4d2_si_stumble_special to "63" , but the Tanks still stagger from the sensor bomb. I imagine this is because Sensor Bombs aren't actually grenades but rather use the same type of explosion as the propane tanks, but given it's still a grenade launcher shooting it... it's kind of undermining the purpose of those two cvars.
I haven't tested other SIs but I imagine this would extend to them too.
While we’re on the topic would it be possible to implement a configurable arming delay on the sensor bomb? In its present state there isn’t really a reason to not use it over the normal grenades.