This article by GDale clearly recommends removing the headrest from this style of DG canopy. It very nearly killed him on the way off.
Quote:
“We are going down really fast. The canopy goes off. The headrest, as the canopy pivots upwards like this, because it [the headrest] is attached on the back [of the canopy] quite deliberately so that it can’t slide back, so it goes ‘boom’. The headrest hits me really hard on the back of the head and puts my lights out. And I’m out for seven or eight seconds. So now I’m going down through 1200 feet in the vertical, glider accelerating, unconscious.”
“If you have an old DG with the headrest here [pads back of his head] take it off and put a roll behind your head instead, because if the canopy does that [again shows a canopy rising nose first, swinging round a point at its back] it will swipe you [10:30] really hard.”
https://members.gliding.co.uk/wp-con...out-advice.pdf