Can anyone here please clarify if the HDD block size change can significantly impacting the speed of large Reverse Incremental mode backup ?

The L: drive where it stores the VBK and .VIB is formatted using NTFS 64 KB Allocation Size.
I've got one Exchange Server backup that is taking 18+ hours for the incremental backup (not even full), and from the screenshot below it shows the Bottleneck is Target which I assume is the Backup Repository drives.

Any help and clarification would be greatly appreciated.
Veeam Support - Case # 01859572