HONG KONG, Sept 21 (Reuters) - Asia macro hedge fund managers, many of whom posted strong returns this year, are betting the Japanese yen's unrelenting slide will end soon and some are even priming for a possible tumble in Japanese government bonds. Veteran Japan investor Soon Hock Chua's Asia Genesis Macro Fund closed its short position on yen recently after the short trade contributed about 3 percentage points of the gross return this year. The Singapore-based fund had a net return of 9.3% at the end of August.