You should refer to paragraph 17.3 of the current ERSA entry for YSSY. It says, among other things, that the 500FT vertical separation design buffer for V1 might be infringed if aircraft have performance problems departing YSSY.
It also says the “wake turbulence standard of 1,000FT vertical separation from heavy aircraft may not always be achievable” when flying in V1. I have never experienced wake turbulence in V1 when flying under heavy aircraft flying into or out of YSSY. However, that’s not the same as saying there are not substantial wake turbulence risks in flying through the same chunk of airspace in V1 in the minutes after the heavy aircraft has transited over V1.