I suspected as much (well, I would say that now, wouldn't I!) but it's good to have it confirmed.
And thanks for the hint, Norm.
On Slo Poke's right hand side, we've welded the spacer to the frame and the hex bar - so that's going nowhere - but I was thinking of making my own removable spacer out of stainless tube, for the left hand side.
A slight issue that we might have is that, in spite of our efforts to get it right, I think the hex bar may 1/2" too far to the right - which isn't causing mechanicals clearance problems - but may be an issue in left hand corners as we run really-really low.
With apologies to fans of full mudguards.

But we have a cut-and-shut solution.

