ASTRA MILITARUM: Missile Misery

Hi team,

This is a competitive list I've played from 8th Ed release until a week ago. It got a bit tense with my WH40k group when I kept winning (6-0), so I decided to play other lists!

HQs (x5)
3x Lord Commissar (all have plasma pistol, power fist) = 195pts
2x Company Commander (all have plasma pistol, power fist) = 90pts

ELITES (x12)
1x Techpriest = 52pts
11x Platoon Commander (all have plasma pistol, power fist) = 385pts

TROOPS (x12)
12x Infantry Squads = 480pts

HEAVY (x6)
6x Manticore = 798pts

TOTAL = 2000pts

TACTICS
- Manticores: Focus fire against high wounds/toughness units in order of priority. With 6 I've killed Gork's and Land Raiders in a single turn. Only four missiles? Not a problem! Techpriest repairing as required.
- Infantry: Deploy the troops is groups of four (one on each corner of an invisible square), with the commissars and commanders in the middle of the square for morale and orders. Keep them around your Manticores until the deep strike threat has passed, then flood the board.
- Commissars and Commanders: The cheaper power fists and the static 'to hit' value in close combat changes in 8th makes these little guys golden. No one suspects 3 S6 AP-3 Dd3 coming from a 35pt model (i.e. the Platoon Commanders).

What do you think? How would you beat it?