no, cro cannot affect HO detections. In your example, after call setup, it’s highly probable that the call will HO to cell B. If it doesn’t, it means your HO parameters were modified.
What you say in the end is already the answer. When you introduce 1900MHz within a 850MHz network, you expect the new band to capture the traffic. So you put higher CRO’s, force HO from 850MHz to 1900MHz and restrain HO from 1900 to 850.
1900 provides better capacity and cleaner frequencies, normally..
But by doing such a “1900” oriented network, you might certainly degrade your radio quality. So you must find a compromise : push most traffic to 1900 (not all), in order to load this frequency band in such a way that the radio quality in both bands are equivalent.
See, loading 1900 at 80% and loading the 850 at 50% might provide equivalent radio quality. (the more you use the frequency band, the more interference)
Optimization of such multiband network is driven by traffic sharing first, and radio quality in second.