Hiu OldBits&Pieces,
The different eBay sites your eBay UK listings are visible on should not vary based on whether the items were listed through Auctiva or through eBay. I don't believe eBay publishes any information about this so I recommend contacting eBay's customer support department to receive a definitive answer to this question.
Any additional questions or concerns? Please contact our customer support team using the appropriate link on our help page: http://www.auctiva.com/free-auction-software-help/help.aspx
-Mike