I would recommend if you have a mech being targeted, because the AI likes to focus fire, run him out of site if possible and/or use the Vigilance a lot as well. Also I don't usually sprint after the first round as you can run into the enemy with them having the advantage.
This is important advice. One reason I like having several jump capable mechs is because you can both generate Evasion and Brace without using Vigilance. I'll also Vigilance and Sprint on my ground based mechs to get them out of trouble.
My feel of the three factors the AI uses to prioritize targeting:
1) How many of its units can focus fire on the target
2) How much firepower the target has
3) How much armor the target has (prioritizing lower)
That isn't a bad set of factors, but it seems to ignore Evasion more than I'd think it should. A Grasshopper with 5 Evasion pips and Guarded should not be the focus fire target, but it often is.
I kicked the difficulty to Target mechs up a notch. Lights 3, Mediums 2, Heavies 1 and Assaults 0. Then I dropped base targeting floor from 75% to 65%. That gave more meaning to lights. They annoyed the crap out of me most of my campaign run as the game use to send in swarms of them. With high evasion they were hell on wheels until I hit gunnery 10. I still can't always precision core out the CT of one even now with an assault mech.
That is an interesting change.
Out of curiosity, how does missile to-hit treat light mechs with that? I'd think that it should result in being able to two shot any light mech by firing a full load of LRMs at it to make it unsteady and then coring it out with a called shot.
Theorycrafting: My missile boat has 3 LRM15, each missile of which generates 5 STB damage. Filling the STB bar takes 20 hits, so it would require on average 45% to-hit to fully fill the STB bar (which guarantees unsteady). Filling it to 80% requires 16 hits, so it would take 35% to-hit to on average fill it to that point.
As this makes clear, even with low to-hit chances, LRMs are lethal to fast movers. Once they are unsteady, they crump to the alpha from a Heavy or Assault mech.