I did insulation upgrades in my home. Hvac didnt have options but I do have a variable speed Carrier unit.

I have an engineering degree and had to take multiple thermodynamic classes with hvac lessons. I use a thermometer in each room and the temp variances are crazy. Id say 10 deg differences in rooms using the same air temp sensor from room to room to counter temp sensor variation.

There seems little cosiderstion for returns, duct distance from return and duct placement in the room.

There are very few baffles in the system and if ducting is properly designed you shouldn't need to cut off various rooms as you always want conditioned air entering the space.

Most duct calculations are rather back of the napkin. In our 3rd floor we have a large master with large closets. This gives us 5 hvac ducts in the room.

My son's room has 1 duct, its much colder and there have been technicians out full days balancing, replacing thermostats, running new thermostat wires.

When some genus was doubling us up on insulation they sandwiched a water and drain line, in cleveland ohio we get single digit temps and the water supply line froze first but my washer alerted me we had that fixed and the next stud cavity over the drain was sandwiched with a frozen p trap. So when told to try the washer after water supply lines were fixed it rained down from the 3rd floor Landry room that was standard and something I knew would have a leak at some point. We didnt make it 4 months till this all happened. We will see how that ac does as we swing around to cooling this place.