Here is a video showing how to open the sheds on a warp wider than that which is usually used for bands.
This warp yarn is mercerized cotton and is smooth and friendly. The sheds open easily.
When weaving even wider pieces with finer and not-so-friendly yarns, other methods are used to help ease open the heddle shed.
The following video shows a couple of methods for opening the heddle shed on wide and sticky warps. It also shows how to open heddles when two are in use, for example, when weaving Andean pebble weave.
And what about the shed rod shed? That shed can be hard to clear too particularly when you are working with wool or very fine warps. The following video shows how I strum my warps to loosen and separate them just enough to be able to open the shed. After the first video segment there is a small clip of Felicia in Candelaria which shows how she strums her warp threads with the point of her wooden tool. She is working on an oblique loom.