Hey galamb,
Your images are correct: from the birds-eye view, the forestock should follow the taper and flare of the bore. 3/32 to 1/8" is a good rule of thumb, certainly no more than that. From the side view, the top edge of the forestock should be a straight line from the breech to the muzzle, about 1/3 to 1/2 way up the barrel side. The bottom of the forestock should follow roughly the line of the ramrod. As you've noted, the ramrod hole may not be parallel to the bore. On these images it looks really exaggerated, but on a completed longrifle it's a good thing to have it slightly tapered. The difference between the depth of the forestock at the entry thimble and at the muzzle may be 1/8", but over the length of a barrel the taper is not noticed. What IS noticed is when the forestock web at the muzzle is really large when it doesn't need to be. That said, the web on my guns is still larger at the muzzle than at the breech - it kind of splits the extremes of having a parallel ramrod vs too much taper. Hope this helps,
-Eric