Goodwill Impairment Proportionate Method – Why only reduce 80% from goodwill?

In a consolidation question, NCI was measured using the proportionate share of net assets method. The goodwill impairment in the (note) was $150,000, but in the goodwill working, they only reduced goodwill by $120,000 (i.e. 150,000 × 80%).

However, I thought under the proportionate method, the entire goodwill belongs to the parent, so the parent should bear the full impairment. So shouldn’t the full $150,000 be deducted from goodwill?

Why is only 80% deducted from goodwill when the parent owns 100% of it under this method? Is this just a working presentation issue, or is there a deeper reasoning?