Photos slideshow layout

If I’m making a slideshow in Photos 4, can I control the layout of photos on a particular slide? If I’m using, say, the Reflections theme, it seems like each slide has a random number and layout of photos. I can change the order of photos by dragging them around the bottom, which seems to re-randomize the layouts. But do I have any control over which layout to use for which slide? I could have sworn I’ve done this in the past.
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Thanks