All 15 past verbs here are on فَعَلَ, but their present forms do not share one middle vowel.
● ذَهَبَ—يَذْهَبُ uses fatḥah.
● رَجَعَ—يَرْجِعُ uses kasrah.
● بَلَغَ—يَبْلُغُ uses ḍammah.
The past weight alone does not tell you the exact present partner. Learn the complete pair with its meaning.