Arc patch - preserve mercurial changesets

When using ‘arc diff’ to create a single review for multiple changesets I can see distinct commits listed in the Phabricator web view.

However when using ‘arc patch’ to add the review to a different mercurial repo get a single changeset and it has additional ‘Differential Revision:’ line added.

How can I use ‘arc patch’ and preserve the distinct changesets ?

‘arcanist 65cda1596f25bb9daea1d78c46402ab61df073d5 (9 Jul 2020)’

This is not supported. See https://secure.phabricator.com/T1508.