Both DY and CF are tracking stocks. that means by design to...

Both DY and CF are tracking stocks. that means by design to align to LYC. In facts there are US SEC regulations. They are allowed to have a spread over short periods but over longer terms the average deviation has to be zero including exchange rate. Mellon bank runs DY and there is info about that on Lynas web site. CF is run by multiple brokers but they to have to work to align as well.
Let me be clear the responsibility to align is in US, for both CF and DY. There is no requirement or responsibility for LYC to track US.

Lets just look at Mellon DY and what will happen next it is same for CF. Fridays close for Lyc was 6.13 times exchange rate of .75 is USD 4.60 DY closed in US at 4,70 so there is a USD 0.10 discrepancy. Mellon should have bee selling out of inventory or even short to keep the price of DY close to LYC on Friday. Depending what is in Mellon's inventory Mellon may need to go on ASX and buy shares before US markets open on Monday in US. This may move LYC up a tinny bit but looking at volume My guess is they will buy 25,000 to 100,000 max.

Day to Day most trading is between holders of LYSDY with Mellon only jumping in when prices get to far out of balance. Depending on what LYC does before US market opens Mellon will add shares to the US DY market. or if LYC goes way up they may even buy shares into their inventory to keep things close to balance. If Mellon loses money on their trading that is their loss. How much they can make is regulated. In 2015 Mellon made too much on their trading and holders of LYSDY received a dividend from Mellon to decrease melon's gains. Because of this you will occasionally hear US traders say D Y pays the Lynas dividend and CF does not. this is untrue they both have to transfer and dividend to the holder of record on the dividend day. The market makers for DY if they make too much will have to pay a dividend just like Mellon did in 2015.
So ASX is totally independent of US the opisit is not true. CF and DY by law have to track LYC.ax Mellon and Market makers have to hold one share of LYC.AX for every share issued of DY or CF. They can also maintain a working inventory.

This is an example not real numbers of how much the average price may deviate all % are absolute deviation. average has prices weighted for volume.
Any one trade 10 %
Average over any hour 5%
Average for any day 1%
Average for week 0.5%
Average for any month 0.05%
Average for year 0.00001%