I agree with Bill. Go all the way up until the bow eye touches the front roller. Even more important than that (and that is important), is that the boat is resting fully on the bunks at the rear, with at least a couple of inches of bunk protruding from the rear. If you allow your boat to "hang" on your bunks in the back, you can have a "hook" form in your boat hull (fiberglass sag from the pressure of hanging off the bunk not supported). I havn't heard of the problem occuring with aluminum boats, but I'm sure it could cause denting in the rear, which would have the same effect - poor boat performance, more than likely porpoising at lower speeds.
By the way, for those who know me.... still not out to sea... but stuck on the ship in port.... we're not going anywhere, but we are "playing underway" for a week.... and since I still have internet access.... I'll be posting during my non-duty hours.
All the best,
cajunram1