Immutability cost increases for Put Operations

[collinp]

We currently have ScaleOut repositories that are using Azure for capacity tier. We pay about $4,500 per month in Azure operations (mainly write operations) for this environment. I ran the Veeam calculator and compared scenarios between our current environment with no immutability and future environment which includes 7 days of immutable storage. The "Put" operations triple when adding 7 days of immutability according to the calculator. Here are my questions:

1) Why does immutability require more PUT operations than usual?
2) What are you considering a "PUT" operation? Here are the Azure listings of operations pertaining to a storage account from the Azure Blob pricing page and I'm wondering what category "PUT" falls under out of these.
Write operations (per 10,000)
Read operations (per 10,000)
Archive High Priority Read (per 10,000)
Iterative Read Operations (per 10,000)
Iterative Write Operations (100’s)
Data Retrieval (per GB)
Archive High Priority Retrieval (per GB)
Data Write (per GB)
Index (GB/month)
All other Operations (per 10,000), except Delete, which is free

-Collin

[collinp]

I think I have these questions answered. My next question is if we currently have 90 days of retention in Azure Blob and we want to add 7 days of immutability, why does the Veeam calculator show triple the PUT operations. If I'm just adding 7 days immutability to our current 90 days of retention I would expect the PUT operations to only go up by 20% (even with the added 10 days required for immutability).