There’s a lot of generalities to frame fit; as the other posters above me have pointed out; but to the OP, you are trying to get an endurance fit on a race frame the Six (and the CAAD) are shorter front-to-back, and intended to be ridden in a more aggressive position than an endurance bike like the Synapse.
To get a more upright, stretched out fit on a Six, you’d need to upsize.
Did you go go into the dealer looking for a carbon endurance bike, and they put you on a Six, or did you go in asking for a Six, and ‘make me fit on it?’