here is a picture of a dish with beams (read lines) from the mirrors to the focus point. The mirror pieces are cracked from a bigger mirror. Take care not to get injured.
The reason for this method was a false mounting. The wholes in the dish allowed to mount it wrong, the upper side was at the right side. It didn't work at all, no focus, much frustration. With the mirrors I found my misteake easily. With the top side on top, all is fine.
It is a little bit difficult to hit the sun but with some trials it will be ok. Follow the beams from the mirrors to the focus, the correct position can be found. It can be used also with a dish and unknown focus point.