Currently Edge, Chrome and Safari have "touch adjustment" feature to select hit targets for touch.

Edge's implementation seems adjusting the touchstart coordinates and target to a nearby target. If the touch events is interpreted as a tap gesture, the mouse events will be implicit capture to the same target.
Chrome (and Safari) only do adjustment when interprets a sequence of touch events as a tap gesture. And only coordinates and targets of mouse events will be changed. Which causing developer feel confuse that the target are different. (such as crbug.com/399761). We are planning to change that.
However, modified coordinates for touch might not be a good idea since the original touch point will be totally concealed from developers. So our plan is adjusting the touch target only and keep original coordinates.

Should the touch event spec mention that UA might adjusting the touch targets. Maybe adding a note to let developer know?
(And there is a similar issue to pointer event spec )