I'll offer upfront that I have neither saddle (use a Toupe), but...
if you sized up with your Romin and it worked, you may not have actually sized up. Rather, you got your size.
If there's a Spec dealer in your area, I'd suggest having your sit bones measured. There's more to a good (saddle) fit than just that measurement, but knowing yours may help you decide.
I’ve had my sit bones measured more than once (Ischial Tuberosity 130) and according to the BG Chart
with my riding position of Aero to Upright I am between a 143 and a 155.
I have used 143 Toupes for years which were just ok, I switched to a 143 Romin in 2011 and after about 3 months of tweaking the position I came to realize that the saddle was not fully supporting my sit bones unless I was in an AERO position. After reading about sizing up the Romin on RBR I tried 155 Romin Evo and found it was comfortable in all positions and have been using it since. It seems a "flat" 143 saddle supports my sit bones where a “curved or rounded” saddle requires a 155.
So you could be right that I “got my size”
Well...right size is affected by saddle shape. Many riders in the pro peloton will ride the Romin in a 155mm and another saddle in a narrower width. I ride both a Toupe and Romin in the 155mm size btw and the Romin does feel a bit narrower. My preference is the Toupe which I believe to ride wider and feels to support my sit bones better because it is flatter. That flatter shape in 155mm width may not be comfortable to someone a bit narrower hipped and why the Toupe 143mm is so popular...the Toupe riding wide for its width I believe.
I am also interested in the Chicane but haven't tried it yet. If the saddle is a bit roundy...based upon what you wrote, I would suggest the 155mm...unless you ride real aero with aggressive forward torso lean.