I'm not 100% sure but my understanding is that yes, the greater the difference between your current level (lets say 35) and the level of what you wanna craft (lets say 15 v/s 34), you have greater chance of having a boosted stat.
Don't forget it's random so you will have to craft multiple times to have the type of bonus you want (+20% (high dura) or stats or rune slot(s))
Craft on bro!