converting PDF to PDF/A increases file size

I had asked about this in an earlier thread:
http://www.aspose.com/community/forums/thread/562315.aspx

And was instructed:
You may used Aspose.Pdf for .Net for optimizing the PDF file. Please check Optimize PDF file size documentation for the purpose. Hopefully it will help you to reduce the file size.

We are now working with Aspose 9.9.0 and I've found something interesting in my testing to pinpoint this issue. 

Using a Word document I created a PDF 3 ways:  Using Word’s built-in feature, Amyuni and Aspose.  It appears that Word creates a PDF that when Aspose converts to a PDF/A it increases in size.

Please see my attachment graphic showing changes in file sizes, and my samples.

Can you shed any light on this?

Thanks,

Kristen Theologus