Here is a picture that will help explain one of my methods. The job here is already finished, so you will have to imagine that the fillet in question is not there, and the red curve is just a rough idea drawn on the surface. Because of the angle, there is no way to project onto this correctly from any of the orthogonal views. So after I've drawn the rough curve, I adjust my viewing angle to that which will work best for the projection. I then draw a line that corresponds to that angle (that's the green line almost hidden among the selected lines). I move that line away from the surface and then I make the plane perpendicular to that line. Next, I copy that line to several points along the rough curve. The lines selected are those lines, which I have extended to fall on the plane. Now I can draw the blue curve between those points. After drawing that curve, I delete the selected lines -- they are no longer necessary. Already, this method washes out a lot of the irregularities of the rough curve, but if necessary, I move the curve's points on the plane until I have a fair curve. Now I can project that curve onto the surface. As I said, even after it is projected, if it doesn't look quite right, I can move the points on the plane again and the projected curve will automatically follow. This is very neat. When I'm happy with the projected curve, I 'Show Points' and move the endpoints to be certain that they are precisely where they need to be. I then use that curve to cut the surface. I'm afraid that this sounds awfully complicated, but when you've done it a hundred times, it goes smoothly. One thing that this method permits is a gap between surfaces that can vary in any way that you choose. It doesn't have to be straight or tapered. It can be narrow at the ends and wide in the middle, or whatever suits the model. I want to mention something else. When you use 'Blend', the bulge factor should be different depending on the angle between the surfaces. But what do you do when that angle changes over the length of the 'fillet'? Simple: At the wide-angle end you will want a bulge factor of maybe 0.8. At the end with the more acute angle, you will want a bulge factor of maybe 1.2. So first, blend the edges at 0.8 and make a cross-section (usually with 'Iso', or just turn the end of the blend into a curve). Delete that blend. Do another with the bulge factor at 1.2. Make a cross-section at the acute end. Delete that blend. If you want to be cute, do another blend at 1.0, and make a cross-section in the middle. Delete that blend. 'Blend' forces you to chop up a fillet wherever there is a single edge. You can now 'Merge' all of the edges that you trimmed to accommodate the 'Blend' tool, and 'join' all the edges so that you then have only two long curves. Select those and all the cross-sections and do 'Network'. Do you get this? You can make fillets that vary in width and vary in bulge-factor and that cover several surfaces! In other words, you have complete control over what you get. Yes, there is some work involved, but there is no way to automate this process and retain this control. And now you see why I say that doing 'fillets' in MOI is a strength, not a weakness.