Richard,
As stated, the 15 stars were for the 15 slave states. The Cross of St. George was because coastal Southerners were overwhelmingly English in descent - actually the South as a whole was mostly of English descent.
There were a large number of these styles of flags (with this cross) submitted to the Committee on Flag and Seal and these flags brought complaints from fundamemtalist Christians as a misuse of the cross of the Christian church, and fron the large and powerful Charleston Jewish community, which decried following a Christian flag.
So when Miles designed what would become the ANV battle flag, he just tilted the cross on its side - plain and simple.
Greg Biggs