those grobs seem to be quite slick, so i would imagine they would glide pretty well
Whilst they might be 'slick' looking, but all that means it they look fast, says nothing about how it should glide. Ever looked at the cross section of a Grob wing, they need a lot of the 'v' in (CL × ˝rho × V˛ × S) too stay airborne because it certainly does not have a lot of Camber, so you could say they don't glide that well. Flown one once too, and believe me, they don't. Also trying to make the field with a 20-30kt headwind does not exactly increase your chances either, so the circuit spacing was probably no further than would normal.
Guys, also remember hindsight has 20/20 vision.