Actually the reticle always stays the same size on FFP. It just appears to get larger because you are increasing the magnification. They usually have a very thin center section and don't usually show up too thick to shoot targets at range.
Yes, technically they do remain the same size. However perception is reality. If it "appears" to get bigger when the magnification is increased the is does "get bigger" as far as the shooter is concerned. I got a great deal on a Swarovski because the owner bought it to put on a bench rest gun. It was an FFP with a standard duplex reticle. He didn't understand what he was buying and once he tried shooting at distance the x-hairs were too thick and covered the area he was trying to shoot.
