Use the pixelTolerance to determine whether to snap to a vertex

src/objectliterals.jsdoc

@@ -491,7 +491,8 @@
  *     which event results in a vertex deletion. Default is a `singleclick`
  *     event with no modifier keys.
  * @property {number|undefined} pixelTolerance Pixel tolerance for considering
- *     the pointer close enough to a vertex for editing. Default is 10 pixels.
+ *     the pointer close enough to a segment or vertex for editing. Default is
+ *     10 pixels.
  * @property {ol.style.Style|Array.<ol.style.Style>|ol.feature.StyleFunction|undefined} style FeatureOverlay style.
  * @property {ol.Collection} features The features the interaction works on.
  */

src/ol/interaction/modifyinteraction.js

@@ -536,7 +536,8 @@ ol.interaction.Modify.prototype.handlePointerAtPixel_ = function(pixel, map) {
       var squaredDist1 = ol.coordinate.squaredDistance(vertexPixel, pixel1);
       var squaredDist2 = ol.coordinate.squaredDistance(vertexPixel, pixel2);
       var dist = Math.sqrt(Math.min(squaredDist1, squaredDist2));
-      if (dist <= 10) {
+      this.snappedToVertex_ = dist <= this.pixelTolerance_;
+      if (this.snappedToVertex_) {
         vertex = squaredDist1 > squaredDist2 ?
             closestSegment[1] : closestSegment[0];
       }