Quoted from 2005 Millennium rules
1. Field Size and Requirements
1.01 A playing-field is defined as being a flat, level area, surfaced to minimize injury and completely surrounded by league approved netting to ensure safety and a size of 55m x 33m. A playing field is to contain at least 25 obstacles which will be placed a minimum of 1.5m from the boundary. The playing-field boundary shall be marked clearly visible and will be placed a minimum of 1.5m from the netting
1.02 A flag station is at least 2 metres wide and placed in the centre of the back boundary of the field
.WPBO 2016 rules
1.2 FIELD SIZE AND REQUIREMENTS
1.2.1. The WPBO standard field size is 45x36 meters with a grid of 3x3 meters (Appendix 1). There should be
at least 35 obstacles (bunkers) used on a layout.
1.2.2. A start base must be 2x1.2 meters wide and placed in the middle of the back boundary of the field.
1.2.3. The playing-field boundary shall be marked clearly and placed a minimum of 1.5 meters off the netting.
1.2.4. Obstacles should be placed a minimum of 1.5 meters off the boundary. The order of the obstacles on the field should meet the official events layout
So the CPPS fields have more bunkers, are 10m shorter and a little wider than early Millennium layouts - which also used 7man format for some divisions.
Bunker shape and size has also changed a lot.