A user is uploading assets for a VRC Efficient reach campaign. According to best practices, what should they include to provide full coverage?

Best practice is to include at least one vertical and two horizontal assets. Efficient reach campaigns deliver across several formats and surfaces, and each has its own shape: vertical suits Shorts and mobile full-screen environments, while horizontal suits in-stream and connected TV. Supplying both means the campaign is eligible everywhere it could efficiently reach people, and having more than one horizontal asset gives the system variety to work with rather than a single option. The general principle behind this and similar creative-variety questions is coverage over perfection. A campaign restricted to one orientation, however good the film, forfeits whole categories of inventory, and the reach goal then has to be met in a narrower and usually more expensive pool.