There are at least 5 different factory A15 pistons, all with different dishes. Because A-series heads are all around 30cc, the dish is used to vary compression from USA 8:1 and 8.5:1 to JDM 9:1

* Centered dish shallow
* Centered dish deep
* Offset dish

Also the shape varies to correspond the chamber design. The Offset pistons enable some quench without flattops. The H95 head is the only one with a larger chamber CC, so uses the smallest piston dish.