As @minatverma says - the audit size is the uncompressed size of the data.
It's actually the answer to the question of how many terabytes the export files would occupy if you exported all data tables to CSV files, not counting the delimiters and counting 0 bytes for NULL values.
This has only a very theoretical correlation with the size of the ROS files on disk. Vertica is a columnar database. Each column , roughly , is one file.
So, if you have, for example, a gender
column that can only assume 'M' or 'F', have the projection ordered by this column first, and the column encoded as Run-Length-Encoding (RLE), this file will not occupy more than some twenty bytes - whether the table has 100 or 1 million rows: The value 'F', followed by the integer 500002 (the value occurs so many times), and the value 'M', followed by the integer 499998.
So, you see, they have little to do with each other: in the CSV file, you have one million times 1 byte for that.