By Wally Pyrah MIDWEEK racing in Hong Kong switches from Happy Valley to Sha Tin for an eight-race programme on the all-weather surface, starting at 12.15pm today. Low draw numbers and fast starts are usually the norm for finding winners on dirt at this time of the year, especially with present weather conditions hot and humid. The two apprentice riders, Angus Chung and Ellis Wong, have been making a big impact in the territory in recent weeks and are worth keeping an eye on during the action, especially with their attractive weight allowances worth their weight in gold in tight and competitiv…