I have grown tomatoes in self-watering 5-gallon planters. Now I am interested in building a self-watering raised bed. Instructions for 5-gallon planters typically provide for an air pocket between the surface of the water in the reservoir and the potting medium above. This air pocket allows oxygen to reach the plant roots.

I have not seen this air pocket recommended in instructions for self-watering raised beds that use a media, such as gravel, to create the water reservoir. Instead, a material, such as landscaping fabric, is laid directly on the media to separate the reservoir from the potting medium. The potting medium is placed directly on the material. I am wondering how well plants grow without the air reaching the roots from the bottom. Does anyone have experience with this?

I know a self-watering raised bed can be made with an air pocket by suspending a platform above the water, as is done in a 5-gallon bucket, but I wondering about those without an air pocket. Are there problems that are unique to these, or can there be?