Hello and welcome to the Seamly forum, @CraftingByJam
I’ve taken to making a line with the length of the armhole curve and the length of the sleeve cap curve with a little line connecting the 2 so that I can easily see the difference between them by hovering over the little line:
You can do this for any curves that you wish to compare.
There are a few topics on creating perfect curves, specifically one by @Krolich and another by @KeithFromCanada - both of which taught me how to do this.