The direction of the charge from the front wall is toward the center of the piston crown - its rear wall falls somewhat further back. This helps to keep the fresh mixture in place and helps prevent it from exiting the exhaust port. This will help roll out the spent gasses and cool the piston crown. These port walls determine where the new mixture goes. In general terms - ports that are more directly opposite each other tend to make more peak power.
Range comes from aiming the charge more rearward.
The combination of these angles and the upward angles of the port roofs shows a wide range of possibilities within any engine. The 295 cc test engine has the main transfer port roofs cut to a 3 degree upward angle. The rear ports are angled at 5 degrees upward. The boost port has its surface cut to 55 degrees - when calculated, the effective area of this port came down a lot because of that steep angle. This overall port arrangement lends itself well to midrange power.