It normally rests on the spare wheel
If no spare wheel it will touch the bonnet obviously, might be worth putting something between the screen edge and metal bonnet
Just nip the hinge bolts back up a bit before driving too fast
If you have never released the screen before be careful and lace some spray oil in the securing bolt mechanism
When starting to try and lower it carefully sway it backwards and forwards a few times to test whether the pins are siezed, if they bend, its not good news, if it feels stiff more lacing of spray oil, soak and test the thing again, a last resort would be to tap the joint with a hammer while holding the screen under a bit of tension to crack off the stick