I do not believe that Ephesians 1:20 supports the view that Jesus is reigning today from 
David's throne in heaven.  Jesus being at the right hand of the Father in the heavenly 
places, with all things under His feet, and being head of the Church are not the same as, 
Jesus reigning on David's throne in Jerusalem.

There are many Scriptural evidences for the Davidic throne not being in heaven today or 
any day in the future for that matter.  

1) The Abrahamic covenant is the first place to begin.  Abraham and his descendants 
(including Jacob/Israel) were promised descendants, blessings, and the land (the Nile to 
the Euphrates river) forever (Gen. 12:1-3; 15:1-5, 18; 17:1-8; 26:1-5; 28:13-15; 35:9-
12; Jer. 31:27-40).  This establishes the foundation for God's people Israel being located 
in the Promised Land forever.

2) The Davidic covenant is the next important place to go.  David and his descendants 
were promised the throne in Jerusalem ruling over God's people Israel forever (2 Sam. 
7:12-17, 28-29; 1 Kg. 2:4; 6:12; 8:23-26; 9:3-5; Ps. 89:36-37; Isa. 9:6-7; Jer. 33:14-
26).  This establishes the foundation for the Davidic king ruling on the throne in an 
earthly Jerusalem.  Christ was announced as the Davidic king by Gabriel (Lk. 1:26-33).

3) The next important area to examine is the time of Jesus' coronation; where He 
receives His kingdom.  In the book of Daniel, the Son of Man receives His kingdom, 
glory, and dominion after the judgment of the ruler of the final human world kingdom 
(Dan. 7:9-14, 26-27).  When this account is compared with Revelation 20, one finds that 
the coronation of Christ as the Davidic king, at which time He sits on the Davidic throne 
in an earthly Jerusalem, has not occurred at this present time (Rev. 20:4-6).  This event 
is yet future.  It is also interesting to note that Jesus did not correct the apostles when 
they asked Him a question with the earthly kingdom in mind (Acts 1:6-8).  The Davidic 
throne/kingdom was always conceived as an earthly throne/kingdom.