I think that the problem is that your preimage is putting the image into the boundary of the table and the whole table is centered by default. The table is not the same as the document -- only something in a TITLE statement or an ODS PDF TEXT = statement would go into the top of bottom of the document.
You can use preimage in a title statement like this:
options nodate nonumber;
ods pdf file='c:\temp\imgtitle.pdf';
BTW, when using images for the preimage tag, I use a Paint program to make sure my image is the size I want BEFORE I use it in the preimage attribute. This is because PDF and RTF destinations convert the image to an internal format and I have always had better results if the image is the right size beforehand.
I don't generally use D3D style with PDF because D3D colors the whole background gray and I don't like the way it looks. I prefer SASWEB or the default PDF style (PRINTER style) with PDF. Just my preference.