D3 V4 Marker on Arc

Question

I want to build an application with D3 V4 and have the following problem: I use a d3.forceSimulation and want to visualize circles. These circles can be connected with one or more links. For drawing the links I use this example.

But I want to have a marker on each link. For that I use this as example. But in my application I have a bigger radius of the circles, so the refX is 70.5. That causes that my marker doesn't hit the arc anymore and I need to adapt the refY-attribute of the marker.

Screenshot:

I have tried to calculate the refY with the Pythagorean theorem in the ticked-method:

d3.selectAll("marker")
    .attr("refY", function(d){
        var dx = (d.target.x - d.source.x),
            dy = (d.target.y - d.source.y),
            dr = Math.sqrt(dx * dx + dy * dy),
            unevenCorrection = (d.sameUneven ? 0 : 0.5),
            arc = ((dr * d.maxSameHalf) / (d.sameIndexCorrected - unevenCorrection));
        var hyp = Math.sqrt(refX*refX+arc*arc)
        var offset = hyp - arc;
        if(d.sameMiddleLink)
        {
            return 0;
        }
        else
        {
            return d.sameArcDirection === 0? offset:-offset;
        }
    })
;

But it still doesn't hit the link.

Can someone help me and show me what I am doing wrong?