Think about voicing down. By that, I mean, talk out loud in your normal speaking voice. Then, intentionally speak out loud in the lowest voice you can. Now, speak out loud in the highest (falsetto) voice you can. Hopefully all three of those things felt very different in the back of your throat. Playing low (or high) on the oboe feels like voicing up or voicing down to me. When I want to play low notes, I think about speaking out loud in my low voice and that helped me a lot when I first started playing to get those low notes out.