Before, by the way I look, I always believe Yonex Ti series have larger head frame (especially width) than cab series.

Strung 3 Ti (1 Ti5, 2 Ti7 light) rackets the past several days. I usually strung all racket with 22*24 combo, therefore, the string tension should be a non-factor as they all the same. After strung them, I compared the head size with a cab10tour, and a cab20 (original, about 10+ yrs old), and I found all 3 Ti rackets are slightly wider than the cab20 (about <0.5cm). I don't think that's because I screw up the string process by putting "non enough" extra force on cross, since all 3 of them, are not any shorter (head frame only, measured from throat gromments to top gromments) than the cab20 or cab10 tour. Also did the comparison with some other non-yonex rackets, such as SOTX woven 4A, Yangyang Tactic 8500, etc. The results are the same: about same length, but Yonex Ti rackets are "wider".

So, am I right about my previous assumption? Or, there might be structure factors involved, such as "widebody", etc?

true. but it also depends.

there are variations among the isometric frames. the Ti-10 and MP100 has a smaller frame size than a MP77 for example. the larger the frame is, the larger Yonex can claim their "sweet spot" to be, for what it's worth.

the head shape of the cabs seems to be all the same. i don't notice much difference in variation among the cabs themselves.

Yes. Most of the cab series racket are oval shape.
Most of the MP/TI/ISO series are small iso shape.
So far (as I know) the ISO 900 has the widest head frame.

Best to compare is when they are unstrung.