I'm not sure if I get your question, but in vowelled texts the ه is actuelly a ة ta'a marbouta so the prononciation depends on the sentence ثَلاثَةُ أقْلام or كُتُبٌ تَلاثَةٌ in the last sentence there is tanwin dama two dammah we read it ah as you said but we write it ةٌ and not ه.