Opening this thread with a review written by Lamberg-Karlovsky from 2002:
[PDF]This review of recent archaeological work in Central Asia and Eurasia attempts to trace and date the movements of the Indo-Iranians - speakers of languages of the eastern branch of Proto-Indo-European that later split into the Iranian and Vedic families. Russian and Central Asian scholars working on the contemporary but very different Andronovo and Bactrian Margiana archaeological complexes of the 2nd millennium B.C. have identified both as Indo-Iranian, and particular sites so identified are being used for nationalist purposes. There is, however, no compelling archaeological evidence that they had a common ancestor or that either is Indo-Iranian. Ethnicity and language are not easily linked with archaeological signature, and the identity of the Indo-Iranians remains elusive.
Although over a decade old, the review gives us a very good run-through of the features in Andronovo and BMAC which have corresponded to various traits found among modern Indo-Iranians. In addition, it provides a balanced account of the culture observed in both complexes. Kuz'mina's The Origin of the Indo-Iranians is a far more comprehensive and current read and I'd refer anyone interested in the intricacies to read it.
Goes without saying the authors' wariness towards genetics was appropriate for 2002, but the evidence-based boon experienced in population genetics since then would certainly warrant a re-assessment of that perspective now.
One interesting theme I have observed in Indo-Iranian archaeology papers is the deduction that the Andronovo-BMAC interactions were, relatively speaking, peaceful. There are fortified settlements in the BMAC, but don't appear to be in response to northern nomads, rather a relic of architectural traditions deriving from their origin in West Asia that were continued for religious reasons (article above). Drawing on H Haarmann's paper regarding the process of Indo-Europeanisation (link), it is reasonable to presume this "peace" stemmed from a lack of agricultural competition between the two (agro-pastoralism vs. subsistence farming).