if the well pressure switch goes with the tank then the second floor pressure would more closely match the well pressure setpoints and the ground floor would have slightly higher pressure. with the tank and pressure switch on the lower floor the lower floor would more closely see the well pressure setpoints and the second floor would get slightly lower pressure.
Pressure increases as you approach the ocean floor.
you can improve water pressure by installing a booster pump or if on a well then turn up your set pressure. If you had good pressure before and now are having poor pressure then it could be many reasons.
Increased water pressure
There is usually a main water valve that comes into the house, locate this valve and turn it down. Installing a pressure reducing valve after water main valve will allow for adjustment of water pressure to proper setting.
A lack of pressure to push the water up.
Larger pipes may be needed to ensure sufficient water pressure. For example, a larger pipe may be needed for sufficient water pressure from the first floor to the second floor of a house.
If you have a new pressurised water system there is a possibility that the added water pressure could cause a leak.
The reason is quite simple. Your water pipes are under your house, condo, apartment, etc. the higher up you use the water the lower the water pressure, because it uses more pressure to move the water up to the 2nd floor than to the first thus weakening the stream of water.
check that valves are fully open
It is dark; little light. A lot of pressure from the water above.
High pressure bottle to the floor. Pressure = force. Cross section
most of the time there's a holding tank at the top