The pin should be in the hole of the adjuster that makes the rig tight
I don't think you can get a good measurement of mast rake with the rig loose as it flops from side to side. If you want mast rake with the shrouds in the 4th hole, need the forestay tight. If you want mast rake with the shrouds in the bottom hole, still need the forestay tight at whatever hole that takes in the forestay.
If you think that the right mast rake involves the top hole in the forestay, then tighten the shrouds. If you can't, then you have to shorten the forestay attachment.
I don't know about everyone else, but my rig is set up so that that last hole on either the shroud or forestay is HARD to get in place; either need a purchase on the bridle wire or someone hanging off a trap wire (or even sheeting the main in tight with the traveler all the way over on that side). The bows flex a bit on the 20; what feels snug on the land can give a bit when you're bouncing around on the water. You can rig it lose to get the mast up, and then tighten later, but tight is fast.