The 93rd Highlanders were equipped with Enfield Rifles, so I think should have a range of 3. Treat them otherwise exactly like British Line, except range f 3, and can ignore 1 flag, or 2 flags vs cavalry.
Glory is fleeting, but obscurity is forever.
The Highlanders really had long-range weapons. But there is no point in exaggerating the bravery of the Highlanders. The truth is that there was no struggle with the "thin red line". The Cossacks (the Hussars did not attack the Highlanders at all) did not even lose a single person. The shooting was conducted from a distance of 500 (!) meters. The myth about "thin red line" was invented by journalist William Russell.