It all depends on what "pan law" you're using. Some techniques will put the waveform at 100% in both left and right, then panning to one side simply reduces the other. Some laws subtract from one side and add that information to the other. Other laws set something panned center at -3dB or -6dB and panning keeps the total energy constant. There's a piece of software I use that stupidly defaults to a pan law I don't like and every time I start a new session with it, I have to change it to the one I do like. If I forget to do that at the beginning and don't corrected till after I've already set up a mix, everything changes.