ok, I just read some about Ma and Jie Ting in 三国志.

As Ma was the vanguard for ZGL and ZGL let him speed up and block Zhang He advancement into Jie Ting. Ma didn't listen to ZGL about put the camp in the middle of Jie Ting's opening and instead put it on top of the South Mountain. Zhang He took advantage and stop the water supply and broke him. So if ZGL was advancing toward Jie Ting but Ma had already lost, Zhang He would have used the middle camp of Jie Ting to treat ZGL as he come to rescue Ma. It would be the exact opposite of ZGL original intention when he send Ma to occupy Jie Ting first. Does Mao really wanted ZGL to fight Zhang He at Jie Ting after Ma lost Jie Ting to Zhang? I wish Mao could explain a bit more about his thinking here.