Data that are available for the lower MMP were collected inductively from the MMP using two different commands (REQFIL and REQDCF). These commands are different than what the Pioneer controller uses to request inductive files from the MMP (REQNEW, and REQDCN).
The subsurface HYPM mooring controller configuration has hard coded defaults for file decimation that can be changed when the controller is deployed (but they are not). These defaults were selected to manage power, data, and transmission time, in a smart way.
When the mooring controller requests a C* or an E* file is does using the REQFIL command. The controller specifies the file name that is to be sent. This is similar to REQNEW which does not need the file name specified. (MMP User Manual_Rev E_September 2008.pdf File Transmission Protocol Appendix J-7).
This means that C* and E* files ARE NOT decimated and represent what would have been retrieved in the card, i.e full data sets.
When the controller request an A* file, it uses the REQDCF command.
From the manual Appendix J-7:
REQDCF - Allows the operator to request a file with a specific decimation Nth line value between 1 and 998 (the Nth scan of data is sent with no bin averaging or alias checks).
Here the controller code supplies the hard coded decimation factor = 50.
sys_data.wfp_eng_decimation = 4;
sys_data.wfp_ctd_decimation = 10;
sys_data.wfp_acm_decimation = 50;
sys_data.wfp_acomm_eng_decimation = 40;
sys_data.wfp_acomm_ctd_decimation = 400;
sys_data.wfp_acomm_acm_decimation = 800;
The MMP decimates the A* file on the fly sending only every 50th line of the A*.DAT file and saves this as A*.DEC in the controller.
Your estimation of ~6m resolution seems correct given that the ACM is configured to sample at 2Hz, the nominal velocity of the profiler is 25 cm/s, and only the 50th sample is being written to the decimated file.