I’m using kopia with Storj (with S3 support).
Works very well, but I like to optimize.
Storj use 64MB per segment:
“The ideal part size for large files is 64MB, so that there is one Segment per part. Using a smaller Part size will result in a significant increase in the number of segments stored on Storj. At large scale, this could impact both the performance and cost of your storage”
Please note that max file size kopia repo is using is about 20MB anyway. Multipart makes sense when uploading large files only.
Because of it multipart uploads are disabled:
Hence adding any multipart tweaking does not make any sense.
What you can do is to try to increase max pack size:
I also think that given info you provided Storj is not very good option as a general backup storage destination as it requires very specifically crafted files uploads. In simple terms it is only efficient for storing large files uploaded in 64MB chunks. But there are similarly priced or even cheaper S3 providers out there without such artificial limitations (myself I use iDrive e2) - at the end you have to decide what you use. In addition Storj with zero free egress (you will pay for running kopia maintenance when files need repacking) might end up relatively very expensive overall when used with kopia.