Lightweight Porch Awnings

SomersetPete

I am contemplating buying a porch awning to fit on my Stirling Eccles Topaz.It seems that the usual sizes are 260 or 390cm, being the length of the roof rail. I would like to purchase the 390cm model and I understand that it is recommended that this measurement
should be the flat length of the caravan roof where the awning fits. My caravan has a flat roof length of just 373cm, therefore the front 17cm of the awning roof would dip down.

Does anyone know if this would effect the fitting of the awning and would it tend to distort the roof when fitted?