I'm not sure how you are picturing "human shields." I don't think it is literally holding a child in front of themseleves as if they are a literal shield like in a cartoon or something. If this is the case, then I agree with you, 13,000 does seem high.
I've never been in war, but the way I am picturing it is by having military headquarters in residential places so that if they get bombed, then a bunch of civilians get bombed at the same time. When you consider how many people could live in just a single apartment building, it makes that 13,000 seem much more realistic.