I am a German student who plans to apply for several Phd Economics (mainly in the US). The 1st and 2nd letters will be written by two professors for who I worked as an teaching assistant. I attended quite a few of their lectures and exams, so they will mainly focus on my academic background.
During the summer and spring breaks I did internships as a research assistant for several German economic research institutes and for a famous economic adviser council. The head of the council is aside from this position also the head of one of the institues where I interned. I consider to ask this professor to write the third letter for me because he could use information of two internships to talk about my research experience. I did not have a lot of contact with him personally but I received good letters of recommendations (around 4 pages over all), that explained what I did there exactly (and so forth), from the institue as well as the council.
Beforehand I would like to hear the idea from other people (who probably have way more experience than me regarding grad school admission) if this third letter sounds like a sound idea.
Best regards