Hi Foxhill,
When I tie a knot with 3 passes like that, I tie the first strand on and then poke and prod that one until all the spaces are even ie the width of two more strands. Once I've tied the three strands on, it is usually pretty tight.
I will go around it all to tighten it a little bit but mainly to tidy it up. To do that, I'll use a fid to tighten and position all three strands at each part and do that all the way around the knot. It works for me, but there are better knot tiers than me around and if someone had a better way, I would welcome the advice.
Incidentally, the knots on both those whips are basically the same. Both have 3 passes. The one on the left has the lighter of the three strands in between the two darker strands. The one on the right has the two darker strands together with the lighter one on the side, which gives that different pattern.
Hope this helps.
Pete