I am unclear about certain aspects of the cropping tool. Why is it that when I choose 1:1, 5:7 or 8:10 the crop frame preserves the ratio when I move the horizontal or vertical side, but when I choose 6x4 or 8.5x11, the ratio is not preserved when I move either the vertical or horizontal side? And why do the first 3 options use : while the other two use X? Is there a way to create a custom cropping frame that is 6x4 that is "constrained" meaning that it preserves the ratio when I move either the vertical or horizontal line? Thanks!