I'm practising the verticals using only diamonds (no quadrants) and joining them together - long lines of them without attempting to write the words of the quote, and I've noticed something.

The top diamonds are of the same size.
I'm running a line between the top diamonds on two adjoining verticals to join them together - like you would to form an N or part of an M.

Look at where the line hits the diamond on the second vertical.
It doesn't actually hit just inside interior of the diamond or along the edge! It runs just above the top edge!

If you run the line right to the top of the second diamond, you get a slightly thickened second diamond.

This is a blow up of part of the original quote :

See how the top diamonds are all a bit bigger on the left hand side?

The extra stroke on top of the diamond either joins to the vertical before it to form an N or part of an M. You can quite clearly see in the blow up that the line has been placed on top of the diamonds.

With I and U, and the ends of M and N the diamonds have 'ticks' on them. It looks like the line to form a 'tick' is extending the edge of the diamond in the normal way, giving it a slightly different angle - you don't want the verticals to be joined in this case.

I've always done my joins by extending the edge of the diamond, not adding extra to the top!

So the diamonds are ending up just slightly thicker than a normal diamond, but certainly nowhere big as a quadrant (which is about 1/3 again the length of a diamond).

What this does is explain why I have had such bad luck tracing the original quote.

Also - this way of running the joining lines may be perculiar to this particular form of Gothic Textura Quadrata. But now I've noticed that it is done, I'll be on the look out for it in the future.