Coming back to this for a moment:
I quite like Iikubo. She seems a bit taller than average and she's quite thin which gives her a model-like appearance.With Harunan in DIY, we can now see that her tallness is a bit of an illusion -- because most of the rest of Morning Musume are younger and, therefore, shorter than Ikubo.
In the clips of DIY from the recent episode of Hello! SATOYAMA Life, we can see that Harunan appears shorter than everyone else in the group. It's kind of jarring, especially after seeing her tower over almost everyone else in MoMusu!
This photo is also an illusion. The Berikyuu members' boots for that costume have very tall heels and platforms while the newer members have lower heels and platforms.
When they all have (theoretically) similar shoes, the height difference looks more like this:
(I tried to correct the original image for camera tilt and lens distortion.)
Due to differences in shoes, posture, camera position, and lens distortion, it's very hard to use group photos to figure out relative heights with any degree of accuracy.
Just to get a semi-accurate estimate, you need to correct for all of these, but it's pretty clear to me that the top photo is strongly influenced by shoe height.
Just to further demonstrate the difference shoes can make, the image on the right has been corrected for the difference: