Pilou's example is a general rule,in this specific case fillet engine fails because you have the seam of the surface that match the "sharpest" part of the ellipse



So you got to move the seam edge in a "neutral" position using plug in : MarkCurveStart

Picture shows my workflow



Pay attention to fig-A- and -D-:you see i moved the seam of the surface,so i can increase fillet radius to 0,3 but if you try with solid -D- you can go until 0,38
Please watch the bottom ellipse after 0,3 fillet...you can see that it starts to be too squeezed..just were you had the first seam edge..



M