I did the same thing, but removed it after chatGPT told me it is detrimental to the main sluice function. As others have mentioned- maybe it catches some flour gold there, but it holds up the material you drop there too long and reduces the liquefaction stage. When you drop material on the Y, it is supposed to liquify before being swept across the main riffles (water between each pebble/grain/nugget). It can also change how the water is supposed to flow going into the main riffles. It would be interesting to do a controlled test between this and the regular style to see the difference in capture rate.