Hi,
What error are you running into when using > 160k?
The max for textsize should be 2147483647.
What does your connectionstring look like when setting textsize?
As Kimon pointed out, the version for SDK and ASE would help determine if this is a known issue.
Docs that may be useful:
Large Object (LOB) Support
From:
Enabling LOB locator support
Regards,
Ryan