When I want to reduce the size of a clip I put the cursor on the line between the clips and; when the appropriate bracket symbol appears, I drag the clip to the left, which creates a gap that I must go back and close.
I tried Alt, Ctrl and Shift key combinations to, hopefully, simultaneously enlarge the adjacent clip but none of those combinations did anything.
It seems like there should be an option to adjust a clip size and cause the adjacent clip to follow suit; to prevent creating a gap; but I haven't found it.