I recently purchased a copy Ray Prouty’s book Helicopter, Performace, Stability, and Control. It was a good buy as it was used, a new copy is over $100. He has a section on ground effect and some good diagrams that address the issue but not the main question of the topic.
Angle of Attack (AoA) is the same for both IGE, and OGE. A specific angle of attack will produce a constant amount of lift (other things being equal). The amount of lift produced is the same for IGE and OGE hovers.
The induced flow through the rotor system slows down when close to the ground, the ground hinders the air from escaping. There is now a decrease of the induced velocity flowing down through the rotor. The blade pitch angle decreases and that causes a more vertical lift component and the vector for induced drag lessens (less power needed). AoA is the same for both IGE and OGE even with a decreased pitch angle, this is because the induced velocity is less.