"The triangular shape is defined from a design using 8 cm-wide boxes for each tube. In order
to comply with this rule, the nominal rear wheel axle must be located within the seat stay
and chain stay boxes. Furthermore, the bottom bracket axle must be located inside the chain
stay, seat tube and down tube boxes. The drawing below illustrates these conditions."
Mais c'est sur que ça ne tient que pour les route parce que dans la meme section ils interdisent totalement les haubans trop bas
"INCLINATION OF SEAT STAYS
The front line of the 8 cm seat stay box must cross the area of intersection between the
horizontal 16 cm-high box and the 8 cm seat tube box. The rear wheel axle must be
contained within the seat stay and chain stay boxes."