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Personally, I scribe the lines I want to grind to and basically work freehand with no jigs. I "set" the angle of the file (or the blade, if I'm using the grinder) by eye, make a few passes, stop to check that I like where things are going... do a few more passes... stop to check again... and so on. A lot of the guys talk about "muscle memory". I rely on that heavile when filing my bevels. I haven't developed muscle memory for using my grinder yet.
When using files, every grind starts off being "convex", but gets flattened out once I have cut in to the boundaries. For example, I cut in a plunge line first starting from the outside edge and working my way to the point where the grinding stops for that bevel (e.g. center line on daggers or the transition line for regular blades). Once that's done to the point I have a well defined start/stop point (ricasso), I start doing the long strokes that carry that angle out for the rest of the blade. Muscle memory usually kicks in before I'm even halfway done with the first bevel, which makes it easier to keep the bevels nice and flat from top to bottom. This also works on recurves, but you end up having to vary the angle slightly (or you'd end up with a wavy center line or an uneven edge).
The point is, you can do it all freehand. Jigs can be helpful, but they can also become crutches. I tried using jigs some time ago but basically found (as you seem to have found) that they don't help as much as they get in the way.