Please explain me how monoecious plants prevent autogamy but not geitonogamy and dioecious prevents both auto and geitonogamy

monoecious plant means one flower has only one reproductive organ in them ie.. male or female. so they cannot undergo pollination within the same flower ( autogamy)
but they can undergo pollination with different flowers of the same plant (geitonogamy ).
in dioecious plants the male and female organs are individual ie.. separate plant altogether so it prevents autogamy and geitonogamy.
thank you