As you know, the Harrison is built on the 333 last. I have both the University and the Flatiron which are also on the 333 last and I really love the longer squared off toe, but I don't find the need to go with a shorter length. I wear a 9D in the 333 last and the 8 last and both fit my foot perfectly. As compared to the 5 last, I wear either a 9D or 9E depending on the style. So for my foot the length is the same, but the 5 last width is more narrow than the 333 or 8 last.
I find that the balmoral brogue 5 last styles like the McAllister and Strand don't stretch/give as much in the width as the 5 last blucher or non-brogue styles and so for the 5 last balmoral brogue styles a 9E fits my foot so much better than a 9D.
Sorry for the rambling answer.
I think this explanation was absolutely accurate. Myself, I have to go with the same width between 333 and 65 just because going to an E sort of makes the whole shoe too roomy but agree the balmoral 65 styles definitely don't stretch much, like he said. Wanted to add though that something like the Neumok (balmoral 65 with a more flexible leather) do have that extra give, so wouldn't recommend the width change for something like that.
Thanks for the info. Just placed an order for a pair of black Harrisons. I might end up selling my Brooks Park Ave. if the Harrisons fit better.