Does he?
His most famous CB conversion is Mascherano, who's a midget. At Bayern he converted Alosno who's not tall, Kimmich - short, and here his first conversion was Kolarov - short, while his first choice this season was Fernandinho.
Outside of playing Yaya there for half a dozen games he's always used short midfielders to be CBs.
I suppose you could count Javi Martinez, but he was mostly injury cover and had played a lot at CB before so it wasn't really a Guardiola conversion, just a stop-gap.
Eric Garcia is taller than Kimmich and Mascherano, who Pep trusted completely at the position, and played against centre forwards big and small. It's not his height holding him back, more likely his age and the unsettled nature of our backline.