Good plan with keeping the units close but cover. However, please don't keep warriors in reserve. Your PO count is already pretty low and you don't want to make it any easier for the opponent if you manage to screw up a reserves roll.
If you intend to bring them from reserves, don't do it through the monolith. If that monolith is taken out, you are screwed as you would've declared that you will bring them through the portal and won't be able to field them ever.
And never underestimate what the deception of playing defensive can do to opponents. They are led to believe its easy but then suddenly, WHAM!! Game over in 3 or 4 turns. At least in my experience.