How to Have Clips Next to Each Other Above Timeline Without Gap?

I am creating a sequence where several shots with their opacity reduced will be superimposed over the primary video. The problem I am having is that I cannot place the shots precisely next to each other without having a 1-frame gap between them. When I try to pull them closer together, one of them leaps to the lane above, as shown in the screenshot. I need to have the clips next to each other so I can dissolve between some of them, which I can't do if they are in different lanes. FCPX 10.5 seems to be full of things that should be simple and intuitive to do but apparently they are not...