At this point the tube isn't creating any obvious issues. Put another way, replacing it with an angle iron would not reduce the footprint.
One thing to note - The clearance areas in the drawing are not 100% correct. There is an area away from the support tube needed for arm clearance that is not shown. That would make an angle a bit harder to fit right at the corner of the triangle.
One thing to note - The clearance areas in the drawing are not 100% correct. There is an area away from the support tube needed for arm clearance that is not shown. That would make an angle a bit harder to fit right at the corner of the triangle.