I think EBITDA is running at an annualized rate of about $170m...

I think EBITDA is running at an annualized rate of about $170m (based on H1 2021). But that's the bull-sh*t EBITDA (per IFRS 16). There's about $33m pa in 'lease principal' outgoings, in the period, but also $5m pa in interest expenses, which given the low debt levels probably all relate to the same operating leases. So that gives us a ridgy-didge (pre IFRS 16) EBITDA of about $130m pa (in round numbers).

If we assume capex of $50m per annum then that gives us pre-tax FCFs of $80m. Assuming tax of about $23m, then we have FCF of about $57m pa.

If we go purely by the cash-flow statement, in the HY, then we have $75m of OCF, less $4.5m released from WC, gives us about $71m of OCF, adjusted for $16.7m of lease principal repayments, gives us about $54m OCF = $109m pa. Assuming $50m in capex, that gives us FCF of about $59m.

That said, I don't like to make too many conclusions on the basis of a HY period.