EMR-A has been redesigned at least twice.  MCS (Multi-faceted Control Surface) concept, where a control surface is contoured, or composed of flat surfaces of various angles, makes another appearance here.  The idea is to place traction and contact area where they matter most, and where we don't want them (in order to channel / direct the user's hand or finger to contact surface and traction where they do the most good), both are reduced and minimized.

For instance, immediately below the bolt catch's lower paddle, EMR-A's lever is left very low profile and free of serrations, because we don't want the finger to wander there where it can do nothing.  Serrations only start where pressure can be applied to press the lever effectively.

The serrated area is divided into 80% shallow V, and 20% straight.  Where 80% transitions into 20% provides a natural index, and more traction, without making the lever any bigger than we want.

MCS (Multi-faceted Control Surface) concept started with the ABC/R, EMR and LDFA, and continues with the EMR-A.  The EMR-A's original design was too costly and it looked like a spoon, but you can clearly see what we were trying to accomplish here.

Yep it's a piece of paperclip acting as a roll pin in the rapid prototype.