I’m not sure about your statement which says bitcoin goes down then altcoin goes down even more. I have never seen that happening in first place. It has always been the reverse case for altcoins and bitcoin. They never match up because the most popular trading pair is bitcoin/altcoin only and that’s why whenever people go for selling the alts then they will do it with bitcoin leading to increased rates of bitcoin and decreased for the altcoins. Thus vice verse case is also true for them.