You're comparing a destroyer to a light cruiser to a heavy cruiser.
Which doesn't explain why Shioi is growing as well, but yeah.
Actually, she is on par with Kitakami... with Mogami she's standing on her tiptoes and with Shikinami she's kinda leaning forward (?) so she look's smaller...
You're comparing a destroyer to a light cruiser to a heavy cruiser.
Just for laughs, I looked them up:
Special Type-II (Ayanami-class) destroyer: 2,080 tons displacement, 118 m long. Kuma-class light cruiser: 5,182 tons, 152 m. Mogami-class heavy cruiser: 13,670 tons, 198 m. I-400-class submarine: 5,307 tons (surface displacement, i.e., corresponding to her actual mass), 122 m.
So yeah - going by ship length it doesn't work, but if you base the fleet girls' heights on the ships' tonnages, Shioi fits reasonably neatly into the progression, being just a bit larger than Kitakami (who seems to be standing up straighter in the picture). Admittedly, Mogami isn't more than twice as tall as they are, but then that wouldn't make much sense for their human forms. People don't have proportionally as wide a range of size variations as ships. :)