This is that issue of Bayesian Shrinkage to a global population mean for conjoint data that has been debated at our conferences over the last 10 years. The findings for CBC have been that Bayesian shrinkage indeed can decrease the estimated differences between people and repondent groups. But, even if that happens, the market simulation results and predictions are usually no better by including covariates in CBC, or segmenting the respondents into different groups and running HB separately within the groups.
But, the issue is even less a concern for ACBC, because there is more information at the individual-level from ACBC than CBC. So, there is less Bayesian shrinkage happening for ACBC than CBC (because there is more certainty at the individual level and less need to borrow information across the sample).
If this really concerns you for ACBC, you can take additional steps to reduce the Bayesian Shrinkage, by increasing the Degrees of Freedom and Increase the Prior Variance assumptions during ACBC/HB estimation. If you follow the recommendations in the software, you'll be getting robust individual-level information, allowing for stable individual-level estimation. You'll be OK.