As the S&P 500 hit its 28th record of the year today, the biggest companies are in charge.

See the S&P 500 Equal Weighted Index for example. It favors the smaller companies in the benchmark more than the market-cap weighted S&P 500 does. Both indexes rose Tuesday, but the Equal Weighted index dropped to one of its lowest ratios in years against its more well-known peer, according to Dow Jones Market Data.

The ratio ended the day at 1.1003, the lowest since May 14. If it slips much further, it will be at a 23-year low.

It's no wonder then that while the S&P 500-dominated by megacaps like Nvidia and Apple-hit a new record today, the Equal Weighted benchmark still sits about 4.6% off its high.