AFAIK the taper is designed to be longer than the crank really uses. If you repeatedly install/remove a crank, it will go a bit further onto the BB every time. It makes sense to leave extra space there, as if the crank bottoms out, you're SOL.

In other words, it's perfectly fine. You'd have reason to worry if the crank went to your green line.

Edit: also, don't hit the crank w/ hammer. Just tighten the bolt hard. That'll push it further than any hammering could, without ruining BB bearings etc.