Stumbled upon this intriguing article by Donald Robinson (building on the work of C.H. Dodd):
The special responsibility of preaching the gospel was exercised by the apostles, whose commission was particularly concerned with an extensive ministry through preaching, and by evangelists, like Philip whom we see at work ‘preaching Jesus’ to the Ethiopian eunuch. The synagogue might be a good place for preaching, or any other audience whose general unbelief or ignorance of God’s saving grace might be assumed. From Paul’s case we gather that a fair measure of disputation and argument might accompany evangelism, as in the synagogue at Thessalonica (Acts 17.3) or in a hired hall at Ephesus (19.9). But the central activity was evangelism, and this was not, apparently, something conducted within the ‘assembly’ of Christians, but, if we may so put it, in enemy territory itself.
from ‘The Theology of the Preached Word’ in Donald Robinson: Selected Works Vol. 2, p143