It is found from analyses about some important Mahayana sculpture's formula to fit with matrix system,
the way to connect vertically with upper-class-units "3step-reducing-join" consists of minimal units.
The specific method is explained from the figure below.
Left area places units before connecting.
The practice to connect with units means sharing of limited circles.
Which circles are emphasized with collars.
Right area places fixed status after this practice to connect with 3units.
Sharing circle sets are 2 types concerning about connecting positions, top or bottom of a unit.
It is able to connect with some units vertically by repeating 2-practice alternately, showing the figure below.
This example of the figure below is showing the status to connect with 4-units vertically.
This example of the figure below is showing the status to connect with 6-units vertically.
