i trackstand with my right foot forward which means im generally trackstanding towards a downhill because of the way roads are paved. What works for me is being conscious of using the hill to your advantage. so i let the hill pull me down and forward but i put a lot of weight on my rear leg to balance things out and smetimes i actually lean a little to the left, this includes my bike. Obviously you want your pedals in a vicinity but i don't stress too much about where exactly because i think it's about shifting your weight and using the landscape too. Ease into it slowly and try to assess how much pressure the back leg will need to exert to keep you from rolling forward. slow, steady, and sensitive, feel it out.