To expand on what Graybeard posted, a smaller objective lens size will allow you to mount the scope lower. You want your scope mounted with a height that you have good cheek contact with the stock comb and when you bring the rifle up to shoot you are looking through the scope properly without haveing to adjust your head to get on the scope. If you buy good optics you'll be surprised how bright they are. Remember, after your scope gathers a certain amount of light your pupil will start to close up to compensate.