Setting render region programmatically

[lauesa]

Through the API, I see I'm able to turn on some variables that activate render_region and crop_to_render_region, but I haven't been able to programmatically set the size of the render region. I have a camera resolution of 3840, 2160 and I'm trying to set the render resolution at 1280, 960 with the following code:

bpy.context.scene.render.border_min_y = 0.3333
bpy.context.scene.render.border_max_y = 0.6666
bpy.context.scene.render.border_min_x = 0.2777
bpy.context.scene.render.border_max_x = 0.7222
bpy.context.scene.render.use_border = True
bpy.context.scene.render.use_crop_to_border = True

However, this creates an image of the original size.