With powerful HID lights you can let then grow big. With fluros it just doesn't have enough power to penetrate very far. If you let your plants grow larger with fluros your not going to have much bud on the bottoms of the plant. Did you know plants double or in some cases triple their size after you start to flower. If you flower now those plants could end up around 2 feet. I'm doubting they will triple in your case because of fluros but bet your ass they will double in height.