Good point...I have 22 of them, so they had no trouble keeping each other cozy!I think a part of the reason this works is that there are 14 of them. I'd be leery of trying this with few than six chicks. I'd also be careful to be sure the temps were at LEAST 50 when you're starting out, and that your chicks have a sheltered place to be out of any winds that may crop up. Oh, and either have a netting or some other way to keep them from turning into quick snacks for any hawks you may have hanging around.
I took a 2x4, cut it exactly the width of my run, then cut the excess pieces and stacked them on top of each other, making something of a chimney effect. The water will pool a little around the edges, if it's raining hard, but my girls seem super happy that we care enough to offer them an alternative. 
