Silvia front bumper problem

[viper2003]

I have recently converted my front end to silvia front end, but for some reason when i put the front bumper on and it is bolted to the fenders and everything else it is like saging, sits lower at the top where the bumper lines up with the head lights there is like a gap, and i am not sure why. IF i left up that part of the bumper it lines up ok.
I did not install a bumper support cause i didnt get one, and my other bumper support usdm damaged.
I have seen plently of people running without bumper supports on there silvia conversions and there bumper sits fine.
Is there something i am missing, i have tried searching and i havent found anything concerning this.

[MakotoS13]

common sense dictates that a polyeurethane bumper lacks the rigidity to keep its form on its own. however, fiberglass has an inherently stronger design wich may account for your observation of cars running sans bumper support.

[Maeda]

two words...

Zip Ties.

[vinhisbored]

zip ties work, but then later on, it might 'bend' the bumper. added a lip onto my car, and had to end up using zip ties, and now its sorta bending, and there's some gaps between the bumper/lip