FHSS - Choosing which contributions to use

Currently looking at purchasing a first home utilising FHSS and wondering if it's possible to choose which contributions to use towards FHSS - e.g. the most recent 50k while ignoring the older transactions.

I have a total of 50k contributed over 4 years - however when I first started contributing I was at the 30% tax bracket, where as I am now (barely) in the 45% bracket.

Trying to figure out if it's worth contributing an extra 5-10k this financial year in the 45% bracket to withdraw with FHSS, and letting the previous 5-10k contributed from my 30% bracket sit and compound until I hopefully someday reach retirement age.

This would be to try minimise the disadvantage of withdrawing at a higher tax rate compared to the initial deposit, while also being aware I'd lose out on withdrawing any interest earned over the few years from the initial deposit. Cheers

Example:

FY26 - $15k contribution
FY25 - $15k contribution
FY24 - $15k contribution
FY23 - $15k contribution

Could I use $5k from FY23, alongside the more recent years, or does it default to the initial 50k placed.