Alien bravery is typically 80 to 110. If you bump all 80s and 90s to 100 you should be good. If you bump them to 110, they will completely cease panicking.
80: low for aliens, panics without too much trouble (sectoid, floater, snakeman, muton, ethereal)
90: medium, doesn't panic that easily (reaper, celatid)
100: high, difficult to panic (chryssalid, silacoid)
110: never loses morale from friendly kills (cyberdisc, sectopod, zombie)
What's actually going on:
80: receives 30% morale loss
90: receives 20% morale loss
100: receives 10% morale loss
110: receives 0% morale loss