In the present optative active there are two forms: (1) that with the modal sign -ιη-, having -ν in the 1 sing., and -σαν in the 3 pl.; (2) that with the modal sign -ι_-, having -μι in the 1 sing., and -εν in the 3 pl. The first form is more common in the singular, the second in the dual and plural.
τι_μῴην (rarely τι_μῷμι), τι_μῷτον (rarely τι_μῴητον), τι_μῷμεν (rarely τι_μῴημεν), ποιοίην (rarely ποιοῖμι), ποιοῖτον (rarely ποιοίητον), ποιοῖμεν (rarely ποιοίημεν), δηλοίην (rarely δηλοῖμι), δηλοῖτον (rarely δηλοίητον), δηλοῖμεν (rarely δηλοίημεν).
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].