yup. it will waste material. but its better than head-striking like crazy trying to start your print on the front-end of the media, which will most certainly buckle enough to catch the deflector and jam the media/scratch your printheads (especially when you're in a rush to print a job!)
which is why i posted the option to add tension by-hand, at least on the front-end. just feed enough excess to get your fingers on it, before starting the print, and apply tension until it is long enough to web through the bar & take-up roller.
so far, i've had similiar issues& successful "tension-fixes" with UltraFlex Wallscapes, Phototex, and any banner material lighter than 15oz