I know bulbs have an overlapping effect with their spread but if you placed more bulbs to either side of those 4 do you think the corals directly under your fixture would get that much more light? T5 shine mostly down without too much spread away from the length of the bulb I think. 
 
Worst case I think maybe towards front and back of the tank they might not get enough but I'd think you should be fine right underneath the fixtures? 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
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