I tend to stick with Medium. I tried hard once, years ago, but I got ruined on the third level when those two cruisers jump in close together. I just can't avoid the AAA....
I beat this on hard... I'm playing on hard right now, in-fact I had 2 beta wing people left.
You tell everyone to form on your wing.... fly towards the cruisers till the fighters come after you turn around and go the other way. When they get close enough to fire missiles tell your wingmen to attack and turn around to wail on them. Rinse and repeat. Then watch the psamtik come in and take care of them... with flak
You also have to learn about energy tweaking. Beating the stupid Ravana was VERY hard. I upped my shields 2 and engines 1, took out the fighters and hid by the crusier then took out the weapons subsystem. It's possible to beat it on hard you just have to learn tactics.