300g of boiled potato holds more water and less actual potato than 300g baked potato.
Simple way to solve this, weigh the pots before you cook them.
A potato is a potato is a potato, regardless of the type, so the precooked weight, and therefore the pp's will be accurate.
My leader checked this with the area leader, and basically, boiled potato etc doesn't change much, weight wise, during cooking, whereas with a jacket, a lot of the water evaporates.
So, a 200g raw potato is 4pp, but weighed after baking will be around 100g, and et voila, 4pp.
Does that make sense?