Swap Ice Flak and Fire Flak positions.
You want Ice Flak to go off as fast as possible to remove any kind of sheilds and buffs. Plus Fire Flak has a long range. Also move the blue mage on the first island back to where the fire flak currently is.
And swap the position of the Ice Turret and Red Mage. Red Mage should always be in the middle to cover all five towers. Would look something like this:
Ice Flak Dark Flak
Earth Flak Blue Mage
Fire Flak Ice Turret
Blue Mage Fire Turret
Also you might want to replace the Fire Turret with something else. Fire turrets are clunky and easy to dodge for most players because of how long the wind up time on the attack and how slow the projectile is.