Hola Charles y David
Thanks for bringing up this topic—it’s definitely one that can be tricky! The main point to remember is that while most -iar verbs do not require an accent on the "i" in their conjugation, there are exceptions, as David mentioned. These exceptions typically involve verbs where the stress naturally falls on the "i", causing it to be accented to maintain the correct pronunciation.
There isn’t a strict rule that covers all cases, which is why these exceptions need to be memorized. As you've noticed, verbs like ampliar, enviar, guiar, and fiar (along with their related forms) do require the accent to ensure the correct emphasis in both the present indicative and present subjunctive forms.
For those learning Spanish, focusing on these exceptions and practicing them in context can help solidify your understanding. It’s great that you’re comparing resources, as this cross-referencing can also aid in memorization. Over time, with practice, recognizing which verbs need the accent will become more intuitive.
Cheers, and happy studying!
Silvia