Shaykhul Islaam Ahmad ibn Taymeeyah 728AH (May Allah have mercy on him) said,

دعاء الغائب للغائب أعظم إجابة من دعاء الحاضر لأنه أكمل إخلاصاً وأبعد عن الشرك

“The supplication for one who is absent has a more tremendous response than the supplication while both are present (Or: than the supplication in ones presence) because this is more complete is terms of sincerity and further removed from shirk.”

Source: Majmu’ al-Fataawaa 1/328-329