Yep, but the risk for short exposures at 1.6pp is fairly reasonable.
Remember (I think) all agencies have modified their training to say that 1.6 PO2 is an absolute maximum. Normally restricted for phases of the dive with low stress and no work (decompression).
My original training said take 0.1 PO2 for any negative e.g.; stress, cold, work, fatigue, etc, form the 1.6 limit.
When Nitrox was introduced into the BSAC training, the maximum PO2 to be used was 1.4, (1.6 for decompression - ADP). This was an adjustment from the 1.6 (standard limit) because of UK environmental factors; cold water, stress (low visibility), work (tidal waters). Also, it had become standard in Trimix diving to use a PO2 much lower than 1.6 for the bottom phase of the dive.
Interestingly, I would suggest that was a good decision if you look at subsequent norms, like a maximum PO2 of 1.3 on rebreathers.
Since Nitrox became normal in recreational diving during the 90's, we have backed away from the 1.6PO2 for anything other than decompression.
You are correct to state that the risk of CNS is a product of PO2 and exposure time. But we have all learned that it is far more sensible to be cautious with maximum PO2 exposures. Dealing with a fitting diver underwater is significantly more difficult than dealing with a bend on the surface.
With PO2, discretion is the better part than valour!