Japanese maples often feature very narrow crotch angles - it is somewhat characteristic of the species. It would be helpful to see photos of the plant to see exactly what is involved, but in general, these tight angles are not of huge concern. And one can use spacers on young trees to extand these angles if desired, although 6' is a decent size for this cultivar and I'd wonder about the age and suitability of attempting to extend crotch angles at this more advanced age.

And where is the graft with respect to the this branching? It would sure help to have a photo :-))