You might be right about that Andrew.
Allowing for memory playing tricks, I seem to recall plotting rogue Gulfs over West Africa, South America and mid-atlantic at one time or another and they showed up clear as a bell when I panned out.
However now that I think about it, and as you rightly point out, there were no spikes.
So the conclusion must be that Polar Diagram is limited and, as you ask, how far therefore is the limit?
John