If you are standing, it is more effective to straighten your arms. You can mainly practice some deltoid muscles (both sides of the shoulders) and the upper side of pectoralis major.

If you push in prone position, it is mainly the pectoral muscle and triceps brachii.

Also, if you stick to your body, your hand is 10KG, which is a little lighter and has a little effect of body shaping and practice. The key is to persevere.