Thanks! It's because I'm quite conservative in my initial estimates. As I stated, the missile is likely longer than the 6.73 meters, somewhere around 7-8 meters. I'm also quite generous in "cutting away" fuel tank for the foldable wings. In reality, they probably take less space.
Yes, it reminds me of the 1970s-80s discussions about how difficult it would be to verify cruise missile range limits, because essentially it's all about the volume of the fuel tank, which as you show is very sensitive to small and hard to observe changes.
Was probably a much bigger problem in the past. Today we know Russia has mastered turbofan technology, silicon fuel tanks, and JP-10 equivalent fuel. That wasn't the case back then and there was more uncertainty about the technological sophistication.