@ericamcphee A huge thank you for all of your replies. It has been said many times before, but it cannot be repeated enough: you are the exponent of an exceptionally generous and friendly community.
And your analysis is spot on. If I improve the upstrokes in the “humps” of the m’s and the n’s by starting them immediately at the baseline and by curving them, the separation with the next letter becomes clearly visible.
Now, in my defence, I will invoke two attenuating circumstances.
First, I blindly relied on the exemplar of father Spencer (see enclosed zooms), in which the upstrokes have almost no left curve. I should of course have consulted more than one source. Lesson learned. I could not find immediately the Barnes from which you shared screenshots book but I did retrieve the exemplar that forum member
@jordantruster posted on the web and, yes, her upstrokes are beautifully leftward curved as well.
Second, when I stared at Spencerian exemplars, the “m” always looked as if it is composed of three exactly identical humps (two in the case of the “n”). Thanks to your posts I now realise that I neglected to take the exit stroke into account. I assumed that, where two m’s or n’s are written after one another, the exit stroke “merges” into the first “hump” of the following letter. Instead, the tiny curve at the baseline which starts the exit stroke results in the connector stroke being a bit wider (1.25 spaces instead of 1).
Now, what I find hellishly difficult where an “m” is followed by an “m” or “n” (or another letter that starts with an upward left curve) is to start at the baseline with the tiny curve (which is oriented towards the right) and then, whilst moving upward, transform the upstroke into a left curve. In the Barnes exemplars that you posted, the connector stroke does not curve towards the left until just before it hits the top of the baseline and goes down at the 52 degree angle. As a result, the first “hump” of the m looks different, depending on whether the m is written first, or following another m or n.
If the connector stroke acquires a left curve too soon, that has the effect of making the space between two letters too small. That’s why I have much difficulty with e-m or e-n letter combinations, such as “tenement” or “Eminem”.
Enough of this nerdy ramble, I now understand what needs to be done in order to improve. Thanks again!