I must apologize I guess I miss understood . I thought your question was on the mortise  and how it came to the forestock . You  have not said if this is a full stock leman  Trade rifle or a ½ stock ?
 If I read your question correctly its:
 does the forestock hold the same dimension IE side to side thickness  forward to the entry .
  Again that depends on the  design  of the stock .
 Normally the forestock will hold the same detention  on the sides and bottom  from the lock mortise forward   .     . Its common also to have a  narrowing to the nose cap , if you have one . This however should be gradual and not abrupt .
 Your lock mortise should be raised above this plain .
The bottom should be rounded  not square  with rounded corners .
 Now what will change is the area right along the barrel when viewed from the top  .  While the dimension of the forestock stay or gradually tapers  in width, in   this area the shape changes  greatly  .
 This would be that for say 4 inches or so  in front of the mortises the wall  thickness will be ?? Say 3/16 ,,, it will then start to narrow down  and within another 8 to 10 inches  be but   a fine line  say of 1/16 
Now how fine that  and fast this gets depends on  your eye and what you like . Keep  again this is the area on both sides of the barrel , just in front of the  mortises , when viewed from the top . This also concerns shaping of this area  with both side having the same contour 
 The later , “common place”  plains rifles, were often  blocky  while the earlier long rifles  have fine lines of grace . . 
 Normally   I figure on   having to take a minimum of 3/16   completely off on  custom stocks . Production kits that’s more to a ¼ as normally they are way to heavy.
 Once you have the lines down  and the shape to what your happy with  you then start the finish sanding or scraping  and boning. 
 Once you  think the stock is about ready to apply stain or oil ,,, that’s when you do your carving or engraving   .
 While it may look as if the carving is very raised , its not . You will find most to be 1/16 or less deep .
 Another thing to remember  is incise carving ,,, is much ,much , much harder then the fancy relief carving  .
 With relief carving a person and make a mistake and simply change the design or clean things up . With incise carving ,,, once you make that line , it very , very hard to  correct   and almost impossible to remove.
With Incise carving  you get one chance , that’s it .
 I once again must apologize as sometimes I have a hard time explaining .  If im still confusing you  let me know and I will  make up some quick “general “drawings