Reach distance is greatly reduced when in Shoulder Surfing mode. This creates a massive disadvantage using this mod for any combat situation.

To recreate, place a Villager in a boat and compare perspectives both openning trading GUI and hitting the entity. You will see that you need to be MUCH closer in Shoulder Surfing mode to do both these things.

I had Optifine when testing this and did it in a single-player Survival world.