My gut instinct is with you in thinking that it's easier to tell people where to stand, but Disney has done a bunch of research on this (which they talked a lot about during the SDL Press Stuff) and it honestly makes sense. Think back to the Red Oven Line on Twitter that everyone made fun of for not being distanced. When you have small markers that tell you to stand in a certain spot, and there are multiple people in that party, they naturally fan out a bit. All of a sudden, your six feet (when surrounded by two parties) becomes closer to 3 feet. Here, Disney is directly telling people where not to stand, ensuring that everyone in the group remains 6 feet from everyone in the adjacent group. While the Universal method will be more common (It's way cheaper to have tiny decals than huge ones), I'd bet that Disney's proves more effective for ensuring proper distancing.