I will show you how to fix it with falloff. Falloffs in Modo are a constraining effect of the tool to an area you specified. In the Falloffs menu you can find it next to the ‘Symmetry’ menu. Choose ‘Linear’ falloff. After choosing a falloff, you can drag it out with the right mouse button. If you want it to automatically align, just select polygons like I did in the image and activate the Scale tool. In the Scale properties, you’ll find ‘Axis Align’, where you can change to which axis falloff it will be aligned to. You can also reverse it if the axis is right, but the direction is wrong with the ‘Reverse’ button.