A nuclear weapon is a fast expanding ball of nasty energy. A meson blast is a pre-expanded ball of nasty energy.
Most attacks are a ball (or lance, in the case of a laser) of energy that detonates with expanding force, crushing and tearing through things, but consuming energy as it goes. That's not what a meson attack is. A meson attack is the closest that Traveller has to a Star Trek transporter beaming down in to solid rock. One moment, there are no particles. The next they're all intermixed. It's a trillion tiny explosions within a sphere (a rather large sphere in large meson gun case).
As it says in Striker. "Everything within the radius is destroyed." If a ship is penetrated with a meson gun, the mesons are interacting with the armor, with the air, with the water, with the fuel, with the people, consoles, wires, pipes, tubes, fried chicken, potatoes and gravy. All of it, at the same time. The armor is on fire, the air is on fire, you are on fire, your skin, your hair, your heart, your brain, all of you.
Big Mesons crit more against smaller ships because the meson radius is bigger, thus destroying more of the ship in one gulp.
Since you're trying to make mesons less effective it's ok to let the screen let some slip through. I wouldn't want them near me at all, personally, which is why I'm content on the screens stopping them wholesale.