Go take a tape measure and measure the distance between your 20yd pin and the cente rline of your arrow sitting on the rest.
Now stand at 2 yds and put your 20 yd pin on your intended "spot". Wher's your arrow gonna hit?
This isn't some "phenomenon" I dreamt up. This is fairly common knowledge.....or so I thought it was. Even if it isn't common knowledge.....it's easily explained, geometrically.
Now....the distance between your arrow and your 20 yd pin may vary, some, from bow to bow......but not enough to allow you to put a pin sighted in at 20 yds on a 2yd target and hit it.
Your arrow .......your sight line (either through a peep or not) down your 20 yd pin ......form 2 lines that come together at 20yds. They are not on the same plane....and the arrow is below the pin sight line. So....the arrow is coming slightly up to meet the line (although it's arcing above the line and coming back down).
At 2yds......it doesn't have enough "room" or "time" to make up the difference. If you aim at your spot with your 20 yd pin (that is sighted in for 20yds).....you will hit low. Period (barring user error).