I don't know if captor is still in development, but if it is.. could you consider adding a checkbox to the settings for repeat last size and pos to only use the last size and pos of the "grab selected region"?
so that if the user captures the screen or a window, you don't lose the coordinates from "grab selected region" to do a repeat last size and pos again:
example:
grab selected region
repeat last size and pos
repeat last size and pos
capture screen
capture window
repeat last size and pos (if checked, still uses the coordinates from the "grab selected region" above)