If the cause and effect of a 'magic spell recitation' changes each time it's used, with no explanation as to why, then it's Fantasy. Consistent use means a rule structure is being applied, even if some authors don't realise it. Some authors are gifted enough to carry all of the information they need in their heads. Advanced science is only viewed as magic providing you don't understand it, NOT because of the time period it's set in. You don't need to know the rules of science to be able to predict the actions of our science laws.
Most people recognise cause and effect without knowing how it happens.
Your reality can have the most fantastic setting, odd exotic characters and beautiful alien sunsets, but it is all governed by a set of rules consistent to that reality. I tend to view Mary Shelley's 'Frankenstein' and Stephen King's 'Carrie' and 'Firestarter' as SF rather than Horror. Publishers and bookshops only see authors and books in pigeon-holes and rarely recategorise them. It just means a good selection of books need to be re-distributed to different shelves. I haven't removed a category.