Trying to keep on top of possible backdoor listing/RTO is a...

Trying to keep on top of possible backdoor listing/RTO is a difficult task. All standard IPO's are properly listed on ASX with the exception for backdoor listing IPO's. Any particular reasons for this? I understand that they do not require to meet certain criteria normal IPO's do. Despite that there must be some sort of a register available. I know the money is made by investing in the shell before any RTO etc is announced but I think there are opportunities at the re-listing day for particularly good ones or getting into Cap Raise through a lead broker. Any thoughts?