No Small, Medium or Large option

I've lost the ability to set the number of Top Sites to display 24, 12, or 6 webpage previews by clicking Small, Medium or Large. The Small, Medium or Large options have disappeared from the bottom right hand corner, all I've got down that end is 'Search History'. Does anyone know why and how to get them back as generally I only like to have the Medium option selected rather than the Small option as I have now. I'm running safari 5.0.5.

Thanks.