I think what you're really addressing here is total fore/aft position which will change the angle of the lower shank of the leg. Is there such a thing as too far forward or too far back in aero? The answer, of course, is yes, but as with all things fit it depends on the athlete and what works best for him/her.
One of the most common issues we see come through the studio for people riding in aero is they constantly do the "typewriter" on their saddle: inch forward to the front of the saddle while pedaling, and scoot back on to the saddle right before falling off the front. Inch forward, scoot back, inch forward, scoot back. You get the picture. For these athletes, the most common cause for this that we see is they're placed too far forward on their bike. I call it tipping you over the cliff. Once you get too far forward, you'll continue to move, or fall, forward until you come off the saddle, or hold yourself right at the tip of the saddle usually resulting in discomfort both on the saddle and your shoulders/neck in the aero position.
People get too far forward both from bike fits and taking advice from those who don't know any better because the general consensus is you move forward to go lower. The further forward you go, the lower you can get in the aero position. It's advice you see given all the time on internet forums like this one, and, while yes, the aero position is accomplished by moving forward on the bike from a traditional road position, simply continuing to move forward to get lower in the aero position is misguided. There is definitely such a thing as too far forward.
Let's take a look at TO's fore/aft from when he came in and you can see the change in his shank angle due to the overall change in his fore/aft position...
Here you see his position in relation to the center of the bottom bracket. Before the fit he's riding right at the tip of his saddle with a darn near 90 degree effective angle at the center of his hip, and he would constantly be moving around on his saddle unable to find a point of balance where he could just sit consistently and ride. After the position change, he was much more balanced on the bike, his position was stabilized, his power output increased, and he was much more comfortable. You can see the other obvious changes the new position created, but to address your question you can identify how the shank angle has changed with the overall change in his fore/aft position. It's not what we measure during a fit to determine proper fore/aft position but, of course, it effected. Hope that makes sense to you.
Jim Manton /
ERO Sports