"Other Sizes" vs "Standard Sizes"

To keep things simple, I offer only five print sizes (and only offer paper prints). This way, when someone adds an item to the cart, they immediately see the size options and prices without having to click again. However, I've just added the 30x45 option to available sizes, which is apparently categorized as an "Other Size" rather than a "Standard Size." So now when someone adds an item to their cart they first have to choose between Standard Sizes and Other Sizes before they get to the size and price list. This distinction is meaningless in the context of my website and probably confusing. Is there a way I can get the cart to treat the 30x45 as a Standard Size? Thank you.