This is not a bioinformatics question and should be closed.

But the answer to your question (you didn't give much context here) is that genotype-environmental interactions do not change or are related in a linear fashion: i.e. this is not explained by a one unit of environmental change results in a one unit of gene expression change. I would argue that this due to the overall complexity of both environmental factors (temperature, humidity, nutrient availaility, etc.) and gene expression responses (other disease influences, overall health of the individual, genetic make-up, etc. etc.).