It can be. However, the shape of the gap, and the distance of the rear sight from your eye will give different pictures for different guns.
Suggestion- get some 12x12 white cardboard, tack it up at 50, 100, 150, 200- then note what your sight picture will look like on each. BTW- a deer, facing you, has a brisket just a bit more than a foot wide (Eastern Whitetail- Mulies bigger) side view, about 36 inches long thru the body.
The range finder built into basic antitank weapons used the size of a standard tank's image in the sights to determine how far away he was. With practice, can work.
What we have here is... failure- to communicate.