The relationship of step, keytop depth, keytop height, and switch travel

Aside from XDA and DSA (uniform profiles), common keycaps are designed like the figure below (Cherry profile):

The green arrows indicate "step". This gives keyboards beautiful undulations. The origin of the step is probably non-electric typewriters like this:

The purpose of the step is to avoid finger interference while pressing:

Old non-electric typewriters have long step, and recent chiclet style keyboards have zero step. Non-electric typewriters have long travel so they require long step. Recent chiclet style keyboards are the opposite.

Keytop depth (near to far) also plays a role. You can avoid finger interference by reducing keytop size of depth direction. This is a big reason why chiclet style keyboards have gaps around each key.

Finger angle also plays a role. The step is useless if the finger is perpendicular to the switch. Therefore R4-R3 step should be larger than R3-R2. The Cherry profile figure above follows the theory. However R1-R1 step doesn't. In this case, another phenomenon is in play. See figure below:

This layout has zero R1-R1 step, and in my experience with many prototypes, this is a bad idea. I felt my fingers cramped in this layout. I felt much better below:

In near rows, the step doesn't play a role. Instead of the step, keytop angle plays a role. The keytop height should be flat in near rows. I have no idea about the theory behind the phenomenon.

BTW all the figures above are created by P2PPCB Composer F360. This is also good for making figures.