Interesting thoughts. I hope others will chime in, also.
A little more history on the evolution of this position:
I've been working on moving forward and down all summer. I'm not the most flexible, and have had ITB/PFS issues in the distant past. Once upon a time (in a galaxy...), circa 2001, I had a pro road-fit done in Boulder as part of dealing with my ITB/PFS issues. I've used that setup ever since. So, I've been slow and methodical about inching into this position---maintaining the same seat height, just rotating it around the BB (and then compensating for the ISM geometry differences).
I used the static tri-fit article
as my defined target position. I finally reached terminus on that two weeks ago...noting that I can't get the pad-drop recommended simply due to parts availability. I've been riding it that way since. Initially I was sitting farther back, and my hips were still in a road position---I felt stretched in the arm pits. Then, I had an "aha!" moment where I pulled forward on the extensions and rotated the hips down. Suddenly, it felt good. Especially over the top of the stroke---still a bit impinged, but much better. I also didn't feel as much like my elbows were trying to slide out from under me.
To relieve the impinging, I raised the seat 1cm which is my first departure from my pedal-box geometry, of the last 15 years or so. That said, it feels very good...actually more like my road pedaling position than it did before the change.
I was also having issues sliding forward on the ISM---I was having to engage upper body muscles to "hold myself in place". Per a previous response from Trent Nix to another "fit critique" (for the same reported problem), I tilted my extensions up 10 degrees (forearm tops are dead-level though---measured). That felt much better, in that I wasn't sliding forward on the saddle. But, once I did that, my shoulder angle felt "too closed"...so I pushed the extensions forward by 1cm. Again, that made a tremendous difference in being able to relax perched on my hips and elbows, with my legs pedaling naturally (sorta like my legs are hanging from fixed points). My torso feels statically stable, now.
The position seems to test "fast" (for me anyway). My house sits on a quiet, rural 7mi loop. I average 21.7mph on 2.75 watts/kg vs. 19.3mph (for 3 laps of the loop) in a standard road position at the same watt/kg. Per the "watts->speed" graph thread
that seems pretty respectable.
The post/video above is the final result. I made no further changes after taking and posting the video and measurements.
Note, I have no issues CURRENTLY with handling in this position. I've been up to 38mph in this setup (not blazing fast, but the fastest I'm likely to see in my local races), and have no nervousness, stability, or handling issues. I can manage standard 90' street corners at TT speeds (22mph) in the aero position provided I can take a decent line (use 1-full car lane on entry and exit). I use the basebar on the street to avoid swinging wide into traffic on entry. I don't know what it would be like 7cm further stretched out, and 5cm more forward.