SQL 2012 :: How To Do Selective Read Of File Stored In File Table

I have a filetable that contains a binary file. I need to do a selective read of the file stored in the file table. I can write a C# CLR function that will open the file, read n bytes the from a starting byte. Or I can write a SQL statement that reads the stream in the filetable into a VARBINARY variable using SUBSTRING beginning at the starting byte (offset from 1) for the same n bytes.

Both give me the same result. However, the SQL statement takes considerably longer to read. I know there is overhead in reading through SQL (interpreted language), but the difference in performance is substantial, and I can only attribute this performance degradation if SQL first tries to "load" the entire stream before it identifies the portion of the stream that it needs to read beginning at the starting byte offset.

I wonder if this is the case or if there is another option to read a stream from a filetable directly through SQL queries that is more efficient.