WP_MEMORY_LIMIT & BackWPUp

Hi,
A couple of my BackWPUp jobs fail due to mem exhaustion.
I currently have the following settings for my sites:
WP_MEMORY_LIMIT = 40M
WP_MAX_MEMORY_LIMIT = 128M

If I manually start a job from the WP Admin UI, it succeeds. However, it fails when executed on a schedule.

One of the sites fails at the start during the DB backup, and fails 3 times, and thus the backup zip file is useless.
The other site fails at the S3 upload part (with a 1.4GB zip file upload). It retries and usually succeeds the second time.

Can I conclude from this that BackWPUp is being restricted by the lower 40MB WP_MEMORY_LIMIT, and that I should consider upping it?

Can you clarify BackWPUp’s requirements in this area please, particularly in respect to WP_MEMORY_LIMIT vs WP_MAX_MEMORY_LIMIT?

Cheers,

Conor