As I mentioned above - I thought you're playing Amateur.
If you are playing Master; your puzzle should look like this:
The solution for above Master is:
Top (L-R): Jackal and jackal.
2nd from top: Falcon, crocodile, lion, crocodile and falcon.
3rd from top: Crocodile, falcon, lion, beetle and beetle.
Bottom row (L-R): Ibis and ibis.
Hint: Do the 2nd and third rows first. Arrange the heads outside the squares (either above or below where you can position the heads - move up-down or left-right). Count the squares, spaces and then get the heads. Then position them at the squares.
Now - your questions as to why it is 8x13 and the solution is 4 rows.
Note that the puzzle is to place certain God's head inside certain boxes-squares in that 8x13 grid.
Those movable squares are 4 rows at the center.
I think those squares have heavy black lines surrounding them.
In the solution above; those squares-boxes are surrounded by green lines.
Tell me if you need more explanation.