Smarter people than I maybe can give better answers, but I know CFKA has touched upon shin alignment during the first few steps of hurdling and how it effects the subsequent hurdles. The hurdles also have a steering mechanism similar to that of a long jumper, so I am not sure if the hurdle would be the answer.
Your mental picture is correct though.
Do you think that an incorrect first step(rolling down) correlates to incorrect last step(premature knee extension), regardless of acceleration length? (although I feel as though it would be amplified with short approach as you have said above)
Using the hurdle should tell you if it’s a guidance/steering problem (don’t hit the hurdle) or an impulse problem (hit the hurdle). The crux is if its a combination of both.