If the frame size 1x1 is selected when you are creating a disc pattern, only 1 small square at a time, of the 1750 squares (50 x 35), will be selected for accepting or rejecting that particular square. So if the 2x2 frame size is selected, you will be accepting 4 squares at a time (2 across and 2 down).
I have used the different frame sizes when creating disc patterns. That is all the different frame sizes are for. When creating a disc pattern in the CTX, the frame size you select will allow you to select 1, 4, 9, or 25 squares at a time . Use whatever frame size is needed to help create/edit a disc pattern. The frame size selected does not have anything to do with the detecting process, only the creation of discrimination patterns. I have attached a screen shot from XChange2, it shows the result of making a selection using each of the frame size options that are available in the XC2 app. The XC2 app. does not have the 5x5 frame size, but instead has a rectangle (that can be made to whatever size you want it by dragging a corner), a 1x1, 2x2, & 3x3 selection. The different frame sizes allow faster editing and the creation of very narrow or odd shaped disc patterns.