I need to clarify a previous misunderstanding regarding sear/disconnector function:
The right sear is connected exclusive to the "in battery" lever. This sear goes down when the bolt carrier is in battery. This sear is controlled, in entirety, by that lever. This ensures that the weapon cannot fire out of battery (and also ensures striker is held back until the bolt carrier and bolt are in battery so that light strikes don't occur like w/ the gremlin).
Since that hole isn't centered (the one in front, where lever connects to the sear), it lowers when lever is pushed down and rises when the lever rises
The left sear interacts w/ both the left (semi auto w/ the hump) and right (full auto w/o hump) disconectors. This controls what the striker does when you pull the trigger. Trigger pulled, striker releases... Granted, with semi auto, the bolt carrier crossing semi auto disconnector requires you to re-pull the trigger w/ each shot, thereby releasing and resetting the trigger.
Here is the left disconnector (semi auto) OE from full auto FCG. You can see the ramp towards the rear that allows it to slide by the sear when you release trigger and the front edge that grabs the sear to trip it w/ each trigger pull:
Here is the right disconnector OE from full auto FCG -- I'm not entirely sure about the function of that front ledge but the sear appears to sit between that and the rear portion which is what grabs the sear and serves to pull it forward (note no angle as it is never forward of sear and needing to slide past). Best guess right now, is that it is a safety function to push/hold the sear up when trigger isn't pulled to avoid runaway full auto... And that foward nub would likely work in both semi and full auto modes based upon its location. Also, being located between the two sears, I think this disconnector plus that forward nub helps to keep the sears and disconnectors in proper alignment.
Here's what the left OEM sear looks like, the rear of that lowermost protrusion (as pictured) is what the disconnectors pull on to lower and release this sear:
And with the disconnectors, when the safety is engaged, it pushes them to the floor of the receiver. So that angle cut would lay flat against the bottom of the receiver when the safety is engaged or not in respective fire mode...