From the FAQ:

A shot has been attempted. Whether this is a three-point attempt is strictly based on the shooters ratio of three-point attempts to non-three-point field goal attempts. The chance that a player has of making the shot is based on his shooting percentage, the assist rates of his teammates, his defender’s stop percentage (captured by defensive rating) and to a lesser extent the other four player’s stop percentages and the block rates of all five defensive players

I know we all focus on the advanced stats and ast%, but if you believe the FAQ it is "assist rate" and not the advanced ast% that leads to an efg bump. IMO and efg bump occurs in the sim at around .625 cumulative assists per minute on the floor, regardless of the ast% on the floor.

Ast% is directly responsible for crediting an assist to a given player, but from my own experience if you have .625 (which equates to 30ast per 48m) on the floor then a bump is very likely. 

In the HDP progressive last season we were using 07-08 and 77-78. I noticed something significant about the difference between a rotation that included Ronny Turiaf versus Amir Johnson. Turiaf has an ast% of 10.8 but an ast rate of .0877, while Amir has an ast% of 5.1% with a rate of only .0377. Turiaf in RL had an efg of 47.4% and Amir had a 55.8%.

When I played Turiaf my ast rate was over .625 and he shot in the 55% efg range, more than 8 points higher than IRL. But when I used the same rotation with Amir instead not only did the entire team shoot worse but Amir had an efg well south of 50%.

I've run into the same kind of issue in the recent theme leagues, anyone else see any results like this?

again... old language that was not updated after the advanced stats were put into play.  It's ast% now.  Verification.

also it's helpful to keep in mind that most of the WiS NBA faq was written by a person not particularly comfortable or adept in using words 

it comes from 2 stocktons and a lebron at C. atleast that is what  2 of my fingers think