it is very reasonable to assume that the 11% of false matches are over-represented in the 268 cases
Pure speculation on your part, there's nothing to support that assumption.
And your claim that the 11% false positives (of all analysis) applies to the subset cases where hair analysis evidence was used at trial? Where's your evidence to support that claim? It's no more than speculation.
You have no more evidence than I do, but at least I have a rational explanation why it's likely to be greater than 11%.