Seen, Sheen (س، ش) ki shakal shuru, darmiyan or akhir men kesi aati hai ? How are the shapes of Seen, Sheen (س، ش) when they fall in the beginning, middle and the end of the words?

Question: Seen, Sheen (س، ش) ki shakal shuru, darmiyan or akhir men kesi aati hai ? How are the shapes of Seen, Sheen (س، ش) when they fall in the beginning, middle and the end of the words?