Hellman (yes as in Diffie-Hellman) invented this idea (chaining a reduction function and a hash together over and over) for the improved time/space tradeoff. Hellman's idea actually predates the terrible Microsoft cryptosystems which are famously vulnerable to it, because too many software engineers don't realise Computer Science and thus Mathematics are applicable to their work whether they like it or not.

Oechslin improved on Hellman's idea to make "Rainbow Tables" by sightly perturbing the reduction function with the depth, so that collisions are fleeting unless they also coincidentally happen in the same position on a hash chain, this makes his Rainbow Table far more efficient/ reliable for the same pre-computation effort and it produces the "rainbow" picture in his slide deck.

For my purpose Oechslin's improvement was irrelevant of course because I actually wanted collisions.

But memory fades, it is possible either that I got lucky, that I actually had 16GB of RAM, or that I made some minor efficiency improvements that were enough to make it work.