Need help with design

I'm unable to find solution any where hence posting here.
I want to make highlighted portion smooth, radius should be 120.
My design is combination of Elliptic Arc, Arc, and line. I want all to be seamless smooth. I've used hard coded values for demonstration purposes.

code

var makerjs = require('makerjs');

function demo(startAngle, endAngle, radiusX, radiusY) {
  
  var example = new makerjs.models.EllipticArc(startAngle, endAngle, radiusX, radiusY);

  
  
  var arc = new makerjs.paths.Arc([35.00000002352587,-69.28203202838824], [20, -89], 120, false, false);
  
  var line1 = new makerjs.paths.Line([20,-89.00000002838823], [18.00000002352587,-109.28203202838823]);
  
  makerjs.model.addPath(example, arc, 'arc');
  makerjs.model.addPath(example, line1, 'line');
  
  var fillet = makerjs.chain.fillet(
     makerjs.model.findSingleChain(example),
     120
   );
  
//  var fillet1 = new makerjs.path.fillet(arc, line1, 20);
    
    this.models = {
     example: example,
      fillet: fillet
    };

}

demo.metaParameters = [
  { title: "startAngle", type: "range", min: 0, max: 90, value: 300 },
  { title: "endAngle", type: "range", min: 90, max: 360, value: 240 },
  { title: "radiusX", type: "range", min: 1, max: 50, value: 70 },
  { title: "radiusY", type: "range", min: 1, max: 50, value: 80 }
];

module.exports = demo;

Start by reproducing the example using makerjs.models.EllipticArc, makerjs.paths.Arc, makerjs.paths.Line, and makerjs.chain.fillet. Inspect how findSingleChain handles the combined model and how the fillet radius is applied. The issue does not define the expected geometry beyond making the highlighted joins seamless with radius 120.