You may want to consider classifying a little larger. I think mine is a 1/4 inch (4 mesh). Your sluice can handle that size just fine.
About an inch per foot drop on the sluice (I wouldn't count the flaring as you adjust that up and down to get more water flow) and yes a bout a 1/2 inch water line up above the highest point of the riffles. Keep it level. (You 'll see a V in the top of the sluice).
Think like gold. Gold is Lazy (Like me). It will take the path of least resistance. Get out in the creek and look up and downstream and think to yourself, if I was lazy where would I be? Find the deepest spot you can and dig down down down. As others have said you may have to work some overburden up out of the way. May as well run that through the sluice too.
General steps:
1. Set up sluice to proper angle and depth (keep the butt end out of the water lol, to avoid this build a wing dam to raise your sluice up further).
2. Fill up four 5 gallon buckets of classified material.
3. Spoon feed the sluice, clean it out after the four buckets are gone (Don't overload it, feed it steady, Have a bucket just for storing clean outs)
4. repeat 1-3 till you can't dig anymore
5. Take clean out bucket home and work them cons. Classify further, to 20 50 and 70 mesh and pan each batch separately, do a little at a time especially with the 50's and 70's
6. Store the gone through dirt until winter, buy a 100 mesh classifier and go through everything a couple of times before spring.
<3 Best of luck!
*Edit* If you are digging down and hitting large boulders and hardpan, you are in the right spot. Keep going down.
