There is no such thing as a "90% buy to sell ratio", because every transaction consists of a buy and an equal-sized sell. You can try to classify each marketable transaction in terms of whether buyers or sellers were more aggressive, but that doesn't tell you anything about the state of the order book and the amount of resting orders that are present. Large portfolio do not unwind their positions by just throwing everything into the market as marketable orders, they put chunk after chunk of it into the order book as resting orders. That can easily drive down the price even if it looks like buyers are more aggressive in terms of marketable orders.