You normally use a flat top piston that sits even with the deck surface of the block to get effective quench. The head gasket thickness then provides the clearance with the closed side of the chamber opposite the plug. As 4speeds4me stated to reduce compression they will put a D-shaped dish in the piston under the plug side of the chamber. To raise compression they will put a D-shaped dome in the same area.

You can get some quench effect with open chamber heads by using a domed piston the extends into the chamber but its not as effective as the flat top closed chamber design.

From your description it sounds like you have standard dished pistons. These will provide very little if anything in the way of quench.