Mid-Acts Dispensationalism or Pauline/General Epistles only also comes from a content-based argument. The thought is that what we see in the Gospels and Acts is transitional in nature. Since Christians do not receive the Holy Ghost as flames of fire above their heads, since there is no time-gap between believing and receiving the Holy Spirit after Acts (1 Cor 12:13 with Eph. 4:4-5) we must read the events of Acts with a different dispensational understanding.
There is also the idea that the Gospels, especially the Synoptics, are Jewish in nature, while the Epistles encompass both Jew and Gentile, who make up the Church. So the Church should be primarily concerned not with the transitional books (Gospels and Acts) but with the books that pertain to them, Pauline Epistles and General Epistles, though usually James is thought to be very early historically and written to the 12 tribes of Israel (Jam. 1:1). James 2 also seems to contradict the Pauline view of justification by faith alone.
In general, these understandings represent a hyper-dispensational view, and have been rejected by both dispensationalists and covenant theologians.