On-demand size limit for same app with tvOS and iOS versions.

We're building an app (single AppID) with both tvOS and iOS versions. The on-demand resources size limit is documented as 20GB, but it's unclear whether this is 20GB per AppID (across tvOS and iOS versions), or whether this is per platform. And if this is per-platform, do iPhone and iPad count as one platform or two, and how about different versions/screen sizes of each device? We're building a video-heavy app, so ideally we'd like to have different versions of on-demand resources for each device resolution and color correction. Thanks!