Elbows drift down from the high position
The overhead elbow position is the key feature; dropping converts it to a standard curl.
Overactive muscles
Latissimus dorsiTeres major
Corrective work
Foam RollLats↗StretchLat stretch (kneeling overhead)↗The overhead elbow position is the key feature; dropping converts it to a standard curl.
Erectors compensate as the bicep fatigues in the stretched position.