From my experience the sluice needs tobe setup for the size and shape of the gold your finding. I had different setups for my sluices over the years for the streams I was dredgeing . it seems that no sluice is perfect for all streams and needs a little tinkering to get it just right.
IMO and based on your picture, the set up would have to be perfectly level side to side as any slight slope cooupled with the variations of water flow over the top, would easily move gold to the low side and down and out of the sluice. Is there more to the sluice than what I am seeing in the picture? What is under the louvers? If there is carpet or v-mat under the louvers, is there a gap between the louvers and the carpet/mat?
Edit:
Answered my own question by looking up the sluice. I think it will work fine but still want to keep it as level as possible. If I was to build one similar to that one, I would make the louvers longer so they are overlapping the next louver below.
So today I tested the sluice with a little bit of paydirt I bought awhile ago and never finished panning and after I ran it I found 4 nice flakes in the sluice and 2 in the tailings.which I think is really good because I used 2 garden hoses for water so it wasn't set up properly but best I could do till I get a pump.