When you've done your 500th plane which really resembles the previous 499.. wing here, tail there... getting a feeling for the correct c.g. -still- depends on flying the thing.
And big surprise, the c.g. will be pretty much on #500 at the point it was on #499, or #333.....
As long as you pay attention to what worked on previous planes, that same point will work on anything of a similar planform.
Most of us are pretty confident with recommending the tried-and-true..,"start at 30% mac.."
Unless your design is really unusual, that will work!