Given the size difference between small molecule antigens and antibodies is it ever possible for multiple antibodies to bind to the same antigen if they recognize different domains on that antigen? When the antigen is a protein rather than a small molecule is it more likely that multiple antibodies can bind?
Not only is it possible for multiple antibodies to bind a single antigen, when that happens, it's more likely to trigger a full immune response.
Here's a description of the concept from a company that sells antibodies for research. To help understand the quote, you'll need to know that the portion of an antigen that an antibody binds is called an epitope.
Because an antigen can have multiple different epitopes, a number of antibodies can bind to the protein. When two or more antigen binding sites are identical, an antibody can form a stronger bond with the antigen than if only one of the antibody’s sites is bound. Antigens with multiple identical binding sites are called multivalent, and antibodies are able to bind it more strongly.
Here is an article that describes, among other things, the importance of clustering in B-cells when multiple B-cell receptors bind to a single multivalent antigen.