You are absolutely right that the high compression ratio is the cause - you end up with a much greater pressure variation in the combustion chamber. (mechanics.stackexchange.com)
Accordingly, small differences in the kernel formation rate or location may produce significant in - cylinder pressure variations [9]. (mechanics.stackexchange.com)
Detection of such a tiny signal masked by much larger pressure variations associated with weather phenomena required the development of special statistical techniques and the accumulation of a long series of regular observations. (scientificamerican.com)