Because of the 315w bat wing is the optimal coverage for this grid and hopefully you got De as they are a better throw of light for the watt, 630 cmh you can get a better ie bigger throw a little more but better overall , but 315w will get you there give or take half a week only because it's 315w BUT cmh spectrum has you covered, 630 guarantees you but you'd want a separate veg or dial down on a light mover or veg outside,
Me personally run an adaptable De 315w wing on 1.45m x0.8m no mover dimmed to 70% DWC year round on house air con