The disks you explicitly create for Azure VMs drives will have their respective speed, independently from the data file sizes placed on them.
On Azure SQL MI General Purpose tier each file created will be placed on the nearly sized disk, meaning the bigger the file - the bigger disk (and faster speed) you will get.
IO performance of Azure Premium disks depend on the disk size. This is explained in the article I shared above.
Hope that helps.
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Oury