This makes absolutely no sense to me!
when the ETH price is down so does the safe gas price goes down,
meaning the miners are willing to get even less ETH for mining > thus the dollar amount is even lower than what they would ask.
When
the price is up, you would expect that they would ask for less ETH, as ETH is more valuable and has a higher $ amount, well ... you're wrong! when price of ETH goes up so does the safe gas price, which means when the eth goes up, not only transactions costs more because the eth costs more, but in addition to that miners ask for more ETH which makes absolutely no sense !!
check the gas fluctuations:
https://ethgasstation.info/