Since you can't do scu dma from vdp1 to vdp2, I guess it goes to work ram. BR uses a 176x112 part of the screen and scales it to 2x for both x and y. But it also covers the upper left part of the screen, so as I understand it it sends a end command, wait until it finishes drawing and retrieve it, clear the FB and starts drawing the main sprites after transfering to a vdp2 layer. I could be wrong, but I guess it has an extra 16 ms delay because of that, while the technique I do is - imo - easier and maybe faster. I draw the transparent sprites offscreen first, so when I retrieve the FB the drawing of that part of the screen will be completed for sure, so I don't need to wait. I will still have to clip/mask the transparent sprites to allow something similar to BR.