Actually, the 
mark written in A encompasses the entire opening sextuplet. However, some of the subsequent marks, which, according to us, are to be interpreted as long accents regardless of their factual length, are of a similar length, which makes us consider this mark to be a long accent too. Naturally, the literal interpretation may be regarded as an equal variant. The mark in FC (→GE), quite significantly shortened, could have resulted from the copyist's conviction about the need to unify this and the subsequent marks.
Compare the passage in the sources»
category imprint: Interpretations within context; Differences between sources
issues: Long accents, Inaccuracies in FC
notation: Articulation, Accents, Hairpins