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.
EMR-A was designed from the beginning to be more compatible with a factory bolt catch. Some ambi mag catches can interfere with the operation of a factory bolt catch's lower paddle, as their levers are quite close to the factory bolt catch's tiny lower paddle. Such a close proximity of two control surfaces makes it difficult for the user to distinguish them without a visual, not always possible especially in low light to no light conditions.
On the EMR-A, the area immediately below the bolt catch's lower paddle has the lowest profile on the lever, in order to create as much clearance as possible, so the factory bolt catch's lower paddle is still accessible.