Having handled a number of these some 15 or so years ago I, along with a number of reputed Ysart glass collectors of the time and a glass restorer, concluded that it was not anything to do with Monart, Vasart or Strathearn.
Broadly speaking you are right that this vase resembles a Strathearn shape, however there was a general conviction at that time that these pieces were not from any of those companies.
You should also find that this one has an oily irridescent surface/finish, which is not consistant with anything recorded to date. These were seen with varying amounts of irridecence in those days.
The workmanship was poor. There also were enough about then to note that the shapes, although broadly the same, differed considerably in the diameter of the rim and the overall height of the vase. There were also other shapes, in the same colourway, that did not conform to any known and recorded.