Id second that notion. Leave meth alone if you can do it if possible. However, this forum is about the proper usage of drugs.
The hole on top of the bowl is for allowing air into the pipe. Without it youd melt the meth but be unable to inhale any smoke in the bowl, because of the lack of airflow. Youll want to load your meth into the pipe through the stem, not that little hole. Its way easier to dip the stem into a bag of meth than trying to handle individual grains and chunks with your fingertips and try to deposit them piece by piece in that tiny hole. I broke a pipe back in the day, trying to push a slightly too-large piece of crystal meth through that hole.
It shouldnt affect hit size drastically unless its way too small, like toothpick size. What will affect your hit size, is how much dope is in your pipe, how fast you are rocking it, and how deep you inhale. If you suck it really hard, youll get a looot more smoke than you would with just an average inhale. Picture the intensity of your average weed hit. Youll get a good hit sucking that hard, but a balls out, hard sucking hit will give you those real giant, dense meth clouds.
If you really want a big meth hit, make a little bong. Humongous hits.