Tangerine Dream and Brian Eno arent historically progressive rock. Tangerine Dream had a period from Statosfear to Force Majuere that they incorporated progressive rock beat with electronic synthesis. Although some of their other output hints at many things from rock to electronic to ambient, etc. The great Kosmiche music of europe is well represented by this time period.
Brian Eno is similar with his Another Green World being clearly progressive electronic rock and a few others around this time period hinting at this album which only includes several members that formed Brand X with out the Eno/Fripp influence. To dismiss much of this as progressive rock is to dismiss your head because you cant see your feet!