On my drywasher I use this type of riffle but it is in reverse compered to a sluice box , It gives a nice place for the gold to settle under the lip , Harder for the air to move material over & out of the box , I have them all the way down the tray.
Just my thoughts.
I envision two potential disadvantages to having an overhanging lip facing backwards on a drywasher riffle. First is that the clean out volume would be excessively large due to the static stack of material trapped by the lip in addition to the normal banked material stacked against it. That static stack would in effect compress and not allow any more gold to penetrate it by displacing waste material and would actually be the cause of the second disadvantage that I envision...potential loss of gold by just ramping over the riffles.
PS Hungarian riffles are all about hydraulics and not applicable in drywashers.