@Golden FleeceSince BHP delegates DRP operations to a third-party, Computershare (UK), there are costs rendered which are passed onto shareholders. It is not the usual scenario where a company will manage their DRP internally.
Key excerpts of the documentation
"The Plan is administered in the UK by Computershare Investor Services PLC (Service) and not by the Company"
"We will use the cash dividend paid to you by the Company to buy new Shares in the Company."
"We do not charge you any fees for joining the Plan but each time we buy Shares for you we will charge you a dealing fee"
"We will deduct these amounts from your cash dividends before buying the Shares."
The currency conversion likely occurs when they deduct their fees from the dividend amount.
I have had particular holdings paying dividends into international accounts and the currency conversion rate has always been provided in the dividend statements, so I believe BHP would do the same when generating DRP statements.
(20min delay)