[Empiricist]

That was a controversial glider designed by controversial designer. William H. Bowlus was not a man of success when it comes to his military projects. All of them were rejected by the USAAF. Bowlus was unable to design the gliders according to world's trends in the glider design. No doubt that the report you linked mentions: "The extremely restricted pilot visibility" among others. That was the same factor as in the other Bowlus' glider called 1-S-2100 Senior Albatross Falcon which was a gliderman's nightmare when it comes to visibility with its claustrophobic cockpit of the design unknown in the world. Bowlus was too much "original" to be accepted by the USAAF. Also his BA-100 Baby Albatross gliders with gun cameras to train air combats were rejected by USAAF.