Ninjaflex bed adhesion

I'm printing Ninjaflex with a Flexystruder on a Taz 4 and the results are generally outstanding. However, on large prints I do experience a bit of warping that can pull corners off the bed and distort the print slightly. I'm printing at 220 degrees onto a 40 degree glass bed. I've tried a thin PVA solution and without and I always make sure the glass is squeaky clean (acetone, windex, etc...).

Anybody have any suggestions about how I might increase adhesion?

I've just been printing today on a glass heated bed at 50C with a thin layer of PVA and gotten excellent adhesion. The hot end is set to 220. Printing at 20 mm/s. The only time I've gotten lifting was when the bed wasn't perfectly level.