The phrase "proportional increase" means that the increase is directly related to the original amount or size. In other words, as the original quantity grows, the increase will also be larger. Full definition
Enhanced reporting of deaths resulted in increases in SMRs, with a greater proportional increase in SMRs for cancer and cardiovascular diseases compared to external causes of death. (bmcmedresmethodol.biomedcentral.com)
Therefore, we chose the highest possible minimum coverage threshold, where the gain in the cumulative proportion of type 1 errors from lower threshold values was greater than the gain in proportional increase of type 2 errors. (journals.plos.org)
But the greatest proportional increases will happen in countries including Germany, Poland and France. (sciencedaily.com)