Why is the copy speed slow?

Question

Storage Area Network

Pretty simple configuration:
9th generation HP DL380 server, two 2.4GHz processors, 384GB of memory. Dual port 8Gb/s FC adapter.
storage HP MSA 2042, 4xSDD 400GB and the rest HDD 1.2TB, SAS 12Gb/s The
optics are connected directly, without switches. There is no other load.

Created volumes on the storage, connected on the server (win2012r2).
I copy the files with FAR. Files up to 25 GB in size are copied from the connected disk to it at a speed of about 900 MB / s. But with an increase in the file size (somewhere from 100 GB), the speed during the copying process drops below 90 MB / s. The minimum that I saw was 75 MB / s. I have an old Iomega StorCenter px12-400r full of regular SATA drives over 1Gb/s iSCSI that gives me 96 MB/s, and it's stable.

While writing the question, I decided to check one more server-storage pair: the server is the same as described above, and the Infortrend DS3024 storage system. The disks there are also HDD 1.2TB, SAS 12Gb/s, link server-skhd FC 8Gb/s So when copying a 200GB file, the speed changed somewhere from 700 MB/s to 98 MB/s. at the end of the copy.

Question: is it normal that the speed drops like this?