ok, now i think i understand about the both frames a little bit more. so i set "MinimapCluster:EnableMouse(false)" at this moment. not "MinimapCluster:SetFrameStrata("BACKGROUND") yet ... i don't know if it's really needed.
yea i feel like i'm walking to the wrong direction ... but it's fun for me at least. =)
i was looking into some addons then i realized about the "Minimap" & the "MinimapCluster". i don't know what it means exactly but when i replaced "MinimapCluster" with "Minimap" in oMinimap, moving the minimap didn't affect the quest tracker's position. (not sure about other elements yet)
maybe it causes other problems but i'm trying anyway.