Command for setting Inline Length has no effect
The reason for this behavior is that DB2 must have enough space for the largest possible LOB locator in the column for the row in the table.  

INLINE LENGTH is not like a VARCHAR where space is used only according to the amount of data.  It's like CHAR – the size you specify is reserved in every single row of the table.  

From the documentation (scroll down to description of INLINE LENGTH integer):


  For a column of data type LOB, the default inline length is set to be the maximum size of the LOB descriptor if the clause is not specified. Any explicit INLINE LENGTH must be at least the maximum LOB descriptor size. 


There's a table that shows the minimum explicit inline length for various LOB lengths, and for CLOB(2G), the maximum LOB Locator size is 312 bytes.  

Therefore, for your table, the inline length must be at least 312 bytes to ensure that the largest possible LOB Locator can be stored.