I started using 255, but the image is clipped. "In Camera" needs more head room to retain highlights. My Betterlight scanning training uses 243 RGB as a start value for setting exposure and I have adopted a similar workflow in CO. It is strange, but if you use CO's Generic curves and set the exposure to 243 and then embed the profile at output, the eyedropper in PS will measure 243 but the highlights seem overexposed. When I use my homemade ICC profile delicate highlights magically appear as do shadows. The In Camera profiles even address the problem with cross polarization...It tames contrast. This process can lead to a minor flattening of the image, but at least non of the detail is missing. I can use to use Edit Lab to edit the profile to increase saturation and contrast in the ICC profile, but I have backed away from this process as inkjet Giclee prints can get too saturated and contrasty when they are coated.