I'm on my 2nd all electric vehicle (now I own a BMW i3). Drones are very similar to EVs. The advertised range is really an approximation. Wind, temperature, your speed; they all effect range and how long the car will operate, sometimes dramatically. If I repeatedly accelerate quickly and operate at higher speed then my fuel (stored electrical power) will rapidly diminish.
Same with a drone. Power required to push an object through the air goes up exponentially with speed. The P4 can go 10 mph faster than the P3. It can accelerate much more quickly. It weighs more. All of these things, especially speed, effect range, time of flight.
The battery is bigger. But it's a compromise, with diminishing returns. compare hovering time of flight will let you know truly differences between p3 and p4 in regards to weight, power and efficiency, and time of flight.