There was consolidation between S&P 1880 and 1900 then some decent buying moving up to 1940. It is these buyers that the market makers are want to flush out and get some really good prices. Given the degree of really really poor sentiment, they want really really good prices. Let us say the average price was 1920. A 5% stop loss puts the S&P at 1825. 1800 would be 6.3%.
If buyers at 1920 will hang in there for a 10% drop that brings the S&P to 1725.