Instead it goes the cropped distance under the clip in front of it.
It's not clear what you mean by this.
On the time line, if the right edge of a clip is dragged to the left, the clip will be shortened. No <shift> required. A ] bracket with two opposing arrows will appear at the cursor when clicking. If <shift> is held down while doing this, a gap will be left between the clip being shortened and the clip that follows.
If you want to leave a gap when a clip is dragged from its left edge to the right, hold down <alt> while dragging. A [ bracket with opposing arrows will appear at the cursor when clicking.)