Who cares if he has enough pressure? That isn't the biggest issue here.
Here is:
Remember this is averages...don't jump down my throat if not perfect...you'll get the picture.
Rotors generally put out about 1/2 inch per hour of water right? (.4 actually..but it varies)
Spray heads are approximately 1.5 inches per hour right?
This means that: In 30 minutes of watering you will put down 1/4 inch of water on the majority of your lawn...and the small 13x13 area will get about .75 inch of water...3 times as much. And, if you do what RVLI tells you, it will be a friggin flood zone with all those heads...
So you say you will water less to make up for it? Won't help, now the rotors are getting not enough water to keep grass green... So you say you will hand water to make up for it? Not exactly an automatic system is it? why bother.
Split it into 2 zones if necessary....doesn't cost much more. If there are other factors determining this...let us know, maybe we have solutions. Good luck.
Sprinkler Solutions, Inc.
Arizona and Colorado
www.sprinklersolutions.net