Just so you know, the official site has pages for the starter gigantamaxes. Cinderace's says this.
>The burning ball at Cinderace’s feet has grown to massive proportions thanks to Gigantamax energy. If Gigantamax Cinderace kicks the ball using its well-honed techniques, its fighting spirit will possess the ball and cause the ball to pursue opponents as if it had a mind of its own.
>Gigantamax Cinderace boasts incredible leg strength—in fact, its legs are said to rank among the strongest of all Pokémon! Even without its gigantic Pyro Ball, it can deliver powerful kicking moves that overwhelm other Dynamax Pokémon.
Also, it's at least 88'7", but I don't know if that includes the ball. If it does include the ball, then that still means Gigantamax Cinderace is like 30-40 feet tall or something. So it really does grow, just not as much as a regular Dynamax Pokemon.
