I don’t know how true this information is, I have never come across this before, but Pakistan was definitely the weaker side and India knew this very well.
If India had 80% still in reserve and they were in a winning position - regardless of the reserve in Pakistan’s kitty - India would have prolonged the war and imposed an undisputed humiliating defeat. Considering how intense the fighting got, even prolonging the war by couple of weeks to a month would have made significant difference. But they couldn’t because they were not in winning position and Pakistan side was fighting well.