Mickey,
certainly you have and I am pretty sure you know excactly what you do when twisting up a string! But, as with many things, "shortcuts" (aka stringboards) have a tendency to "steal" some former commonly present knowledge from persons - by just being there - convenient as they are - taking care of one (two etc.) parts of a task. And honestly, why messing with a stringboard when you don't do 50 strings a day? Keep it simple! Somehow difficult for me to explain what I mean - sorry! Read between the lines please.
Anyhow, if you are aware of what you do - okay - otherwise I suggest going step by step - taking care of every single strand.
As far as "perfect" goes:
Anybody ever noticed that bowstring yarn has an initial twist to it? If you mix your bundles and lay the yarn in different directions - some will open up, ?fray and some will thighten, as they should, when twisted to a string. I think there are some boards out there where you cut both ends open and not only one!? And then the above mentioned may happen ...
I prefer to cut every strand for his own, arrange them to PARALLEL bundles, initial twist oriantated alike of course. Tapered ends are no problem at all, just put them together that way ...
BTW: No offense intended in any direction with my "perfect" statement above!