The Total Starch Kit can accurately measure starch levels as low as 1% w/w.
Leaves are likely to have "normal" starch, i.e. Low levels of amylose (and thus not high resistant starch either).
You could easily analyse samples with just 5-10% starch without diluting the hydrolysis mixture after incubating with alpha-amylase and amyloglucosidase.
The AMG has a tiny glucose content, so you would need to allow for that.