I think since you are confused yourself and it's your policy and your contracts, then your clients are going to be just as equally confused. The only thing which is clear, is that your policies aren't. LOL

I would send an e-mail where you clearly state which days you are expecting full pay as a stat day, which days you are considering vacation days and so on. If you aren't sure yourself, then really, you can't expect your clients to be. Spell it out for them.