I have found a nice hack to the 10cm rule is what grip you run on the extension. Running smooth round only makes it tougher. If you have the little “tab” or the pistol grip other hour and pursuit riders use sometimes you can learn to hold the bar in the last finger or two of each hand and gain reach and height.
There are track picks floating around of this stuff.
My new off the shelf extensions are like that and I can grip with my pinky and next finger of I like. That’s like 1.5” horizontal and 1/4” vertical gain versus a full hand death grip.
Also note the TT and pursuit folks don’t rest their elbows on the pads. It is closer to a bit of forearm. Triathlon folks usually rest the elbow all the way on the pad, an Ironman is 4+ hrs ride versus one hour.
The best pics of that are Drag2Zero and their ergo UCI legal bars compared to the triathlon bars. It explains it perfectly.
So, if you get used to riding holding your weight on the forearm instead and using the last fingers on the extensions.....good dimensional fit gains against the UCI “box”.