Since IAST #145 features this treasure of a tangle (click here for all of the delightful details), I thought to write up a few notes from my study of it ~
In my alternate approach, I connect lines to both of the smaller curves before I fill them in. This alleviates the "hit or miss" of trying to get the curves and lines to match up and I can make slight adjustments more easily.
See if it works for you...
In the meantime, join in the fun and send in your tile.