Do eSATA enclosures determine the maximum throughput or is it determined by the HDD and SATA bus specs?

I have an older hard drive enclosure with an eSATA port. I have tried a SATA II and SATA III drive in the enclosure but is only connecting to my machine at SATA I speeds (1.5Gb/s) even though the eSATA port is on a SATA III bus.

My understanding is that eSATA is a direct connection to the SATA bus so I am assuming the drive and bus should sync at the lowest common denominator. e.g. SATA II drive connecting to SATA III port via eSATA should sync at SATA II speed of 3Gb/s.

Or can the enclosure itself be limited to 1.5Gb/s SATA?

If the enclosure is limited to 1.5Gb/s could soldering wires from the a sata cable directly to the eSATA port, thus bypassing the enclosures PCB solve the issue?

There seems to be so much knowledge in this forum.

Can anybody answer OP??

Vague description... model of enclosure? Full model of drive? Checked machune BIOS set up?

_________________
Hard Disk Drive (HDD), Solid State Drive (SSD, SATA, NVMe, etc), USB Flash Drive and RAID Data Recovery Specialist in Massachusetts

I agree with labtech that you should provide a more precise description, as well as the enclosure and drive types.
Are you telling about speeds in reading or in writing ?
There is also a significant difference between maximal speeds in theory and in the real world.
Small hard drive buffer as well as many other factors can influence the speed.