So the initial offering starts out at roughly $25M worth of stock, if I've understood correctly, held by the financial institution issuing the ADSs on Incannex's behalf (Deutschebank?).
Each ADS a US investor purchases corresponds to 50 IHL ASX shares held by the financial institution. If the US share price climbs, arbitrage will have the ASX share price climb to remain close to IXHL / 50. (IXHL being the intended IHL NASDAQ ticker).
I'm pretty sure if demand for IXHL on the NASDAQ looks like it will outstrip the holdings of the ADS issuing institution, it will simply buy more IHL on the ASX in order to be able to offer more IXHL ADSs on the NASDAQ.