My question is does it matter where the cold air return is located, and will it effect the heating of the house?
Yes it will.
In a heating system the cold air return should be at floor level. That's not to say in the floor but usually they will be mounted on a vertical wall at floor level.
Warm air from the heat vents will rise toward the ceiling leaving cooler air settling down toward the floor.... the law of nature. The term "cold air return" is for that reason to draw the cooler air from the floor level and return it to the furnace to be heated. If the return ducts are at ceiling level this will draw warm air returning to the furnace.
The other reason to have the cold air return vents down toward the floor level is to help with circulating the heated air coming from the warm air heat vents.
Since warm air rises you don't want all the warmth at the ceiling .... most people don't live on the ceilings .... you want it at the level of the room where you are.
This helps preventing stratification where you would have a cold zone at floor level then different layers of warmer air rising with the warmest being at the ceiling.
The cold air return at the lower point of the room will help draw the warm air down providing the heat where it's most desired.
If you will be adding air conditioning one method that's being done is adding two return air vents ... one at the floor level for heating and one at the ceiling for A/C with dampers that allow you to close off one of the ducts and open the other so that the system can work to its maximum in each season.
Hope this helps.