Much slower SFTP transfer speed

I have switched from ES file explorer to Material files for a few months, And I realize theres a significant difference in file transfer speed.

Test environment:
SSH server

• Raspberry Pi 4B 2GB ram
• Ethernet connection
• 240GB SSD less than half filled
• OpenSSH_8.4p1 Debian-5+deb11u1, OpenSSL 1.1.1n 15 Mar 2022

Test file: a 448MB .ts video file

Material files starts slow at about 500KB/s, as indicated by the system network activity (theres no transfer speed in the notification, just transfered/total infomation). Then raised the speed to about 2 MB/s. I have waited until the number settles. The system network activity meter has a refresh interval of about 5 seconds

On the other hand, ES file explorer has a transfer window stating the file transfer was done at 52MB/s. The system network activity meter agreed with it, saying that it was transfering at about 54MB/s.

And I have confirmed the speed by using termux and sftp. Also >45 MB/s

For download speeds, theres also quite a difference.

• Material files: N/A, system: 4.6MB/s
• ES file explorer: 55MB/s, system: 59.8MB/s
• Termux sftp: 47MB/s, system: 57MB/s

Material files transfer at 2-5MB/s fluctuating, but never reaches above 10MB/s

Why is there such a difference?

Reproduce the reported SFTP upload and download comparisons using the listed Raspberry Pi, OpenSSH, 448MB file, Material Files, and Termux setup. Trace the app's SFTP transfer path and compare its behavior with the working clients; done means identifying the cause of the throughput gap and addressing it with verification against these measurements.