I doubt that Epicurus considered any aspect of "grasping" something to be part of the canonic faculty. Recognizing a pattern as significant and deserving of attention seems to me to be one thing, while interpreting it - in any way at all, as a snake or a danger or anything - seems to be another thing, and the part where error can enter in.
And it looks to me that it was important to Epicurus to keep separate the part where error can enter from the part that we accept without question - else we have a feedback loop and lose the ability to distinguish between our opinion vs what Nature is relaying to us directly and precognitively.
Well said!