With cadian, and used as screens, I would shift from a short range / non LOS mix to a longer range shooty mix. In your troops. Since you are rich in antihorde, maybe focus on making the troops a valid anti-marine threat (in current meta that's never quite a waste) while preserving their anti-ork potential, at least some.
so a plasma gun (2 S7 or s8 out to 24 inch, using your intrinsic rr1) and a heavy bolter (3 shots direct sight, but s5 with -1 ap and can kill a whole marine a hit.) This way, you don't have to make the infantry move, necessarily, to get into flamer range, and when you have already perhaps locked fields of fire down on a target, you can reroll a lot of stuff while shooting at it at +1 directly.
That's really the only thing I can think of to tune you to the doctrine directly, it gives you a few dead marines at range, potentially, where before, your lasguns didn't affect them. It means you kill a couple fewer orks -- if the orks happen to be inside 12 inches -- but I find when only one unit per side can overwatch, putting an overwatch specific weapon like flamer into each infantry squad wastes points, especially for a doctrine where the troops like to sit on their butts and shoot.
While I know cadian mortars can be very good, screens don't have the luxury of hiding behind LOS all the time to use them, so I reckon go with the bigger guns.