The Segments link tool renders handles above all segments of the link (as determined by the link connector). It accepts four additional arguments, which can be passed as an object to the link tool constructor:

redundancyRemoval boolean If the user arranges two (or more) segments so that they lie on a single line, should the middle one(s) be considered redundant and removed? Default is true. Note that this setting is not applied until the user actually moves one of the segments in question; this means that segments can still be arranged in this redundant fashion, using the link.vertices function, for example.
segmentLengthThreshold number The minimum segment length for which to display a segment handle (to prevent the handle from overflowing its segment). Default is 40.
snapRadius number While the user is moving the segment, from how far away should the segment snap in order to arrange itself in line with another segment? Default is 10.
snapHandle number If the snapRadius option is set to true and the segment is snapped in place while the user moves the segment handle, should the handle follow the user pointer or should the handle stay snapped with the segment until it un-snaps? Default is true, meaning that the handle snaps with the segment.
stopPropagation boolean Should be events stopped from propagating to the paper? Default is true.

Example:

var segmentsTool = new joint.linkTools.Segments({
    focusOpacity: 0.5,
    redundancyRemoval: false,
    segmentLengthThreshold: 50,
    snapHandle: false,
    snapRadius: 10
});