When comparing the proper position for spotting different exercises, you can conclude that, in spotting any exercise, it is important to

Have proper posture which will minimize your chance of being hurt if the need arises for your to help the one for whom you're spotting the exercise.

Moreover, it's also important that you pay close attention to the person you're spotting to see and check if he or she will need help anytime soon to be spotted or not. This is something many spotters can miss and is at the same time a crucial aspect of spotting.