Looks like this missing the exp-kernel, assuming it should be something along the lines of:
def reaching_object_position_exp(self, env: LiftEnv, sigma: float):
"""Penalize end-effector tracking position error using exp-kernel."""
error = torch.sum(torch.square(env.robot.data.ee_state_w[:, 0:3] - env.object.data.root_pos_w), dim=1)
return torch.exp(-error / sigma)
https://github.com/NVIDIA-Omniverse/Orbit/blob/d75e7ff63bf08b558266d2eff42fd4db15d29d6b/source/extensions/omni.isaac.orbit_envs/omni/isaac/orbit_envs/manipulation/lift/lift_env.py#L399-L401
Looks like this missing the exp-kernel, assuming it should be something along the lines of: