I haven’t tried an A3 series drive in such an enclosure, but I have tried a 5S, a 6S and an A1 series drive.
Scanning in an external enclosure works fine, but the amount of samples dropped will be higher than when scanning on the same drive internally.
This can be seen in the reported scanning interval (which should ideally be 1.00 ECC but is more likely to be around 1.13 and higher) at the end of the scan.
The more samples dropped, the higher the scanning interval will be, and the lower the total (and average) PIE/PIF values will be.
This is important when comparing scans made on an internal drive and an external drive, since the total PIE/PIF will be artificially lower on the external drive that drops more samples.
Drives using other chipsets (not MediaTek) do not drop nearly as many samples so the disctinction between internal and external is not important for scanning drives using (most?) other chipsets.