What you're observing is that futures reflect price changes almost instantly, but it takes a bit of time for the trades to be reflected on the tape... makes it look like futures lead, but neither does. I don't believe there is any effective way for retail screen jockeys like us to arb this. (I tried several years ago, but no joy.)
%% Well that worked well in 1987+ plenty of other times.....; +no wonder it pays no dividends ,like SPY/ liquidity leader. JAN up also leads/forecasts the market also; except in 1987......... LOL. JAN up[SPY] ;52 week forecast has worked about 80% -88%/+Thanks.,