Didn't know this would be Thomson approved. Do you think you were able to perceive any riding differences from the change in the effective seat tube angle (if you were able to disregard the reach)?
It is absolutely approved by Thomson for both Elite and Masterpiece versions. I think it is written in the specs somewhere and they will OK it by email.
I found through trial and error that i needed to get my knees way ahead of the pedals to keep my knees happy as they are both lacking ACL's and have quite a bit of osteoarthritis in them. It made for pain free(well as good as i can get it) cycling and it does feel like the effort is more effective and i extended the reach to suit.
I can't say that i noticed any untoward effects of mounting the saddle a lot more forward, than might be considered normal. No handling or comfort issues.
I wanted a bit more forwards, and to have the clamp in the middle of the rails , so i got an Enve 25mm set back post(I think Enve officially OK reversing this post too, but it has been done by many without probs). The pleasant surprise ,with this post , was the extra comforrt the carbon post gave. It flexes less than the Thomson, but definitely absorbs road buzz better.
The above is my fit and along with short cranks, and modding shoes to set my cleats further back, has been something i have done to help my situation. For someone else it may be a different case and not feel at all comfortable, or suit their physique, but I always think these things are worth a shot even if you are just curious. You never know, but it might unleash some hidden watts, or put an end to a niggle.
Both the Thomson(Elite and Masterpiece) and the Enve have been used offroad on typical byways and bridleways we have in the UK. Both have taken a few big hits, when i got the timing wrong, and they have been absolutely OK. If the Enve, or chinese copy, is of interest then don't fear the older 1 bolt clamp posts.
The suggested torque value of the clamp bolt is way too low and you can wind the clamp up way tighter, to keep the saddle in position. Obviously there is a limit because you might burst the post and stick to ti, or steel rails, with this clamp. The newer two bolt clamp is a much better design and they don't need the extra tightening, the single bolt clamp needs., and you could use carbon rails.
edit to add....forgot to say that the carbon Hope posts are another that can be used in reverse. I think i am right in saying that they also OK it as a thing to do. Either way it has also been done by ithers without probs. There is a contributor to Cycling Weekly who uses a Hope setback reversed who tipped me on the Enve.