On the topic of domes, the RG pistons did have raised domes from the factory.
the 9.7:1 pistons have a raised part of approx. 6.7mm, the 8.7:1 pistons have a dome of approx. 4mm and the 8.3:1 pistons have less dome that that.
Note: all rg pistons must be flycut, the cutouts actually extend fractionally below the level of the block, ie. below ehere the flat top of an 18R-C piston is.