I've grown marsilea hirsuta on 1.4WPG (T5 with good reflectors). It stayed pretty small, 2 inches max, but closer to 1.5", and grew quite densly. My marsilea hirsuta behaves strangely, though. It has retained a mostly four-lobed structure, whereas most hirsuta will convert to a 1-lobed structure when under water. Could be the lower light levels that has caused this.