For example, today SPY decreased -3.17% and therefore the 3x Bear SPY ETF, SPXS, increased 9.85% - roughly equivalent to 300% inverse (310%).

What if you somehow foresaw the decrease early in the morning, and wanted to load up on SPXS, would the price still represent roughly -300% if you purchased a large notational value (equal to more than 25% average daily notational volume).