Before you start slicing and dicing on the flare, watch how the materials move down the sluice. The areas between the riffles should be clear or nearly so in about 10-12 seconds. Any less time and you've got too much water flow which will keep the gold from settling out allowing it to blow out the discharge end of the box. Sluicing is about control of material size, angle and water flow. If the riffles are not clearing out then you stand a chance of packing them up with materials. in this case you either need to increase the angle, increase the flow, or slow down on your feed rate. Once you learn what works best for your setup, getting it back to what you need will be much easier.