Yes, there are some “non standard” sizes that make up some of the groupings – that is because it would be impossible to make balanced groupings out of ONLY “standard” size canvases. In fact, if you look at the groupings that the major labs offer – they often contain these odd sizes for that same reason.
Some common misconceptions about “odd” sizes are that:
1) You cannot sell these odd sizes in a grouping because you don’t offer them on your a la carte price list. This is simply not true – I don’t have to offer an 11×13 for sale individually just because there is an 11×13 in some of my wall clusters that I sell as a group.
2) Your lab only offers standard print sizes and will not print these odd sizes. Also not true (in most cases). In the case of every major professional print lab in the US anyway, canvases can be printed in almost any size you choose. In fact, in my lab H&H’s ordering software the height and width of the canvas is done in a dropdown in increments of 1 inch. If you cannot figure out how to order these sizes from your lab, just give them a call- as I said all the major labs (H&H, Millers, WHCC etc) allow you to do this, you may just need to call them and ask how to do this in their ordering software.
That said, if you really do not want to offer the pre-made groupings that come by default with the app feel free to hide them and create your own! If you are an iOS user you can hide them by double tapping on their thumbnail image from the +display menu and set the toggle to “hide”.