For Tai Po, I would at least separate village-house duplexes from conventional estate flats, then narrow further by the exact locality. District-level comparisons are too broad when access, layout and condition differ. I’d also avoid treating an advertised reduction as the final negotiated discount.
Is HK$25,470 supported by comparable signed rents, or is it an asking-rent estimate? Also, does the tenant pay any recurring property charges, or do you? Those two facts matter more than fine-tuning the maintenance percentage. For a country home, I would separately investigate access, drainage...