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The fulcrum is on an imaginary line that goes through the center of the the steer tube and extends infinitely from both ends of the steer tube, so IF if the hand position is the same (I'll take your word from that example that it is, I can not do the calculation myself because there is no angle given for the 70mm stem ), then the relationship to that fulcrum is also the same.Physics would actually tell a very different story. It all comes down to the amount of leverage the rider has over the opposing force of the front wheel. The pivot point of the shorter stem is lower and closer to the fulcrum (head tube/steer tube) providing significantly more leverage over a longer and higher stem with a flatbar.
The mistake you are making here is the same one that lead to power curve cranks.