Resonancebot micro (Hard/hardest)

Hi all,

I've consistently beaten resonancebot in hard/hardest with an early castle drop and by damaging its economy.

Because my main goal is improving my own microing skills, I'd like to beat the bot by letting it boom. This way it can develop an army, putting up a considerable challenge.

Particularly, the AI's ranged unit microing is the biggest hurdle, and I can't keep up with it. I've tried to play very defensively with walling and counter-units, but it doesn't seem to be enough.

What are some succesfull ways of improving army micro? How do you deal with 20-25 skirms who spread out across a large area while you are controlling a "Git gud" works too, I guess.