AC Vent Register Type Based on Room Location

I recently been reading up on vent placement regarding to heating and cooling a room. I am not a complete noob, but not a professional either. I asked the HVAC contractor about it, and I am not sure if he is telling me a bunch of bs. I currently live in the Atlanta area in the south where heat is mostly a problem in the summer. With that said, in most rooms, I have a door on one side, two windows on the other side with 2-way registers between windows. What I find odd is that if I partially close the registers some will blow towards the window, and others will blow towards the room. I am not sure if this is by design or if it matters, but which direction is correct in your opinion? Would you think the room should benefit from a 3 way register? I have seen in northern parts of the country it is best to blow towards the windows, but I am not sure if the same applies to the south. Also, in one room with a similar design as the others, they installed a 1 way register and have it blowing towards the room. Is this correct? If not, would you correct to match the other rooms? Last, when entering the house literally there is the supply side grill with a 3 way register in the wall across the hallway of the return register installed with a 1 way grill pointing towards the floor under the stairs that goes upstairs. I don't know if the HVAC guy mixed up the supply duct and return duct or installed the wrong grill/return. Either way something is off. If given the option, would you have the supply under the stairs or in the way across the hallway? To add some details the house is a 2 story house with a crawl space and an attic. We have one unit for the upstairs, and another for the downstairs. Thanks you all for you advice.

source https://hvac-talk.com/vbb/threads/2236385-AC-Vent-Register-Type-Based-on-Room-Location?goto=newpost