Your well pump doesn't know how long the pipe is. It just knows that it's trying to maintain a certain amount of pressure back at the pump.

What's hitting you hard here is what is known as "friction loss". Basically, the water is "rubbing" the inside of the hose, and the net result is a loss of pressure. The amount of pressure loss is a function of how much water is flowing (usually measure in gallons per minute), the diameter of the hose, and the length of the hose.

I'm going to guess that 1/2" diameter copper pipe roughly estimates the losses you'll get in a garden hose (the hose losses are going to be worse, especially if you're using 3/8" hose rather than 5/8").

So if water is flowing at 3 gallons per minute, you should be losing about 6.5psi of pressure FOR EVERY 100'. So in a 500' run, you could easily be losing over 30psi of pressure.

Another thing to consider change in elevation. For every 10 ft in elevation gain, water loses about 4psi of pressure. So if your trees are 20 feet in elevation above your pump, then your losing an additional 8psi in pressure regardless of hose size.