2. wrinkle shrink film: we are glad to advise that we believe this problem has been solved on our side. The problem had nothing to do with technique, oven temp nor time of heating. It was just the circumference of the shrink sleeves was too big. Therefore, it had to shrink too much and thus, you have the wrinkles.
Since then, we have already reduced the circumference and not get a tighter shrink wrap with very little wrinkling compared to the past.