Bases, for the most part, are irrelevant, as distances are measured base-to-base, and templates are defined as affecting the model if their base is touched. Parallel 25mm bases allow a little give, with regards to templates, therefore, we have placed most models in that category (Orcas, Vulkans, etc.) on 40mm bases just to make for less "it ain't touching the base, so it's not affected" type of arguments.