Why is the letter "Ba" in "Bismillah Al-Rahman Al-Rahim" written elongated at its beginning, and not short?

It was mentioned that the elongated Bāʾ in "Bismi Allāh" (In the Name of Allah) compensates for the elided Alif from "Ism" (Name). It was also said that it is because it was the first letter written in the Mus'haf (codex of the Qur'an), so it was fitting that it be magnified.