Flash does not scale with level

[Raist]

Probably because the stats that enhance it's potency scale in much larger increments across 55 ilevels versus 10 Character levels.

Think about it. If it's primarily bound to a primary stat like say STR or otherwise something like the weapon damage and then enhanced further by STR or another stat, you are likely going to see potency ramp up more when you increase the item level by 40% compared to just the character level by 20%.