http://www.sidecar-industry.com/techpages.htm as a picture is worth a thousand words. So, if you put the light tubes back on your bike after shifting the rear wheel to the left then you might find the same toe-in measurement to be present, but the effective toe-in--defined by the three contact patches--will be different. IMHO, of course.
But anyway, you've tested the rig and it's handling to your satisfaction so enjoy it! I'd keep an eye for wear on that third wheel and see if it starts trying to tell you something, tho.