Since you're using the 4x20 Dominos, you'll set your plunge depth to 20mm though it will only plunge 10mm. 4mm Dominos are awkward to offset (putting more in one side than the other).
You can use the video's technique (thanks, Shane!) to place a mortise in the side of the ply. It'll be 10mm up from your reference line if you put the base on the reference line. If you use the marks on the base that indicate the center of the mortise, you can place the Domino face down with that line through those fence marks to center the Domino. I think the latter is what you want for the mortises into the face of the sides where the 1/2" stock will be joining it.
For mortising into the middle of the edge of the 1/2" spreaders, you'll need to set the fence height to 6mm, which works on paddle fences. If you have pins, you'll need to grind a bit of the fence or put an offsetting shim under the fence.
For joining the 3/4" sides to the 1/2" ply, the best thing is to use the fence in both cases. Tip down the fence and set the thickness to 20mm; the mortise wil be 10mm down from the fence. Mortise the edge of the 3/4" sides as you usually would. To make the matching mortises in the 1/2" face, put the Domino face down with the fence registered to the edge of the 1/2" ply so the mortise is 10mm from that edge. When you join, they should be flush.
Hopefully I didn't misunderstand what you're creating...