Here is side by side comparison of the commentary of Bailey (white, left) vs Munro (colored, right) on this same section. Compare how Bailey categorizes the entire discussion in terms of "thought" while Munro does not mention the words "thought" or any variation of "thinking," but deals with the subject as if it is just another variation of sensation, not something different in kind.
I also added underlines in Bailey which emphasize where Bailey is presuming his conclusion in his description. In passages marked 2 and 3 I also question the presumption that it is necessary for sensation and thought BOTH to be "set in action" and "stirred" by emations from outside. Yes as to sensations, but why does the action of the mind have to be in reaction to something OUTSIDE. I see no reason whatsoever in the rest of Epicurus to think that the mind cannot generate its own actions, and I would presume as devoted as Epicurus was to "agency" that the mind DOES initiate its own thoughts, in addition to responding to things that it perceives, just as we in this thread are both initiating our own comments and responding to the comments of each other.
Bailey is insisting that in all cases the the receipt of images in the mind and the receipt of vision by the eyes are linked together in result, and I certainly see the passage that he is referring to it, but by no means does it follow (in my view) that this process is going on in *everything* that our minds think.