How do you determine the highest melting point with a group of ionic compounds

On my last chemistry test, there was a question about melting point with ionic bonds. But there was no mention in class, the book, etc. of how to determine the highest melting point. Formulas online are more complicated than my understanding. Is there a way, using the periodic table, to know if an ionic compound has the highest melting point (in comparison with another)?

I know that AlF has a higher melting point than NaF but why?

Thanks

Generally, the higher the charge separation, and the closer the cation/anion are to each other, the higher the melting point. The reason why is that as the charge separation increases, the ions will be more strongly attracted to each other, and as a result, will be more difficult to separate in a chemical reaction, and hence, will have a higher melting point. Take AlF for example; aluminum has a charge of 3+, while that for fluorine is 1-, so the charge separation is 3+/1-, while that for NaF is 1+ for Na and 1- for F, yielding a charge separation of 1+/1-. Since the charge separation is greater in AlF, then it will most likely be the substance with the higher melting point due to stronger ionic bonds and intermolecular forces.

In addition, the distance the ions are from each other is another factor, but is not as important as the charge separation. The closer the ions are to each other, the more easily they can interact and form a bond, as is the case with any ionic bond or any bond in general. However, the charge separation IS THE DECISIVE FACTOR for determining the strength of the bond and intermolecular forces, and hence, the melting/boiling points.

Thus, AlF should have the higher melting point due to a greater charge separation than NaF.