Not done processing yet (will be 4k60 when it is), but even at 360p, you should be able to see what's going on:
Source: https://www.youtube.com/watch?v=CK7vXk82MjY
With low numbers of opponents it's usually not hard to keep them off a combat vessel's PP, but with sufficient focus fire, someone is going to have a clear shot. It's one of the reasons most of my hybrid vessels (aside from my Vulture or anything using EPTs, for obvious reasons) can keep regenerating through malfunctions.
Does make sheilds down combat that much more risky and defensive than it would otherwise be.
You can't put phasing and scramble on the same weapon and phasing pulse disruptors cannot induce malfunctions through shields.
Once shields are down, scramble will build up to an effect threshold at a rate based on damage (or possibly size, I'm not 100% sure) then cause a malfunction to a random module on the hemisphere of the ship it last hit. It doesn't need to hit anything specific to do this.
Pulse disruptors need to actually strike the module in question, so penetration depth and breach chances come into play. A pulse laser cannot penetrate to hit a corvette's power plant except from above or below the ship at a moderately steep angle, or perhaps dead on from the rear. The vette's core internals are quite well protected from the front and sides. Anyway, if they have the angle to meet the required depth then the per-shot breach chance comes into play, which is dependent on percentage of hull remaining; 100% hull means the weapon is at minimum breach chance, 0% hull means maximum, and I believe the slope between is linear.