Seeking help with CMS and DRL location with EEGLAB

[anvita]

Hello,
I am new to EEG signal processing with EEGLAB and have encountered some challenges that I need help with.
To give you some context, I used a Biosemi 32-channel Active Two system with a 10/20 setup to collect the data. This cap includes CMS and DRL. However, I initially did not adjust the default settings, resulting in a data set with 271 channels due to unedited channels.

Here are my questions:
First, when importing the data, "Load data using BIOSIG" pop-up should I leave the "Channel list (default all)" or change it? As my file is based on a total of 37 locations, with 32 channels along with the mastoids (2) and other EOGs (3), without CMS and DRL. Do I need to insert these two locations as well? If so, where and how do I find their coordinates, as I cannot find them in the 32 channel cap_coords files with locations?

Referencing the Data: When importing the data, should I reference it? The "Load data using BIOSIG" pop-up mentions "Reference chan(s) indices - required for BIOSEMI." I am unsure about the indices. If I leave this field blank, it warns, "WE HIGHLY RECOMMEND THAT YOU CHOOSE A REFERENCE CHANNEL IF THESE ARE BIOSEMI DATA (E.G., A MASTOID OR OTHER CHANNEL). OTHERWISE THE DATA WILL LOSE 40 DB OF SNR!" What should I do?

Channel Locations: I plan to use average referencing later, but the list of channel locations (.elp) file I made does not include the CMS and DRL information. How can I load my data correctly, and where can I obtain the channel locations for CMS and DRL?
I appreciate any guidance you can provide on these issues.
Thank you for your help.
Best regards,
Anvita

[Coen]

Reference the data. After referencing, the locations of CMS and DRL are not relevant anymore.

Best regards, Coen (BioSemi)

[anvita]

Thanks a lot for your reply and help, Coen!

Can you please clarify, should I reference with any particular preference? Can I reference with two Mastoids or should it be any one channel (Cz)?
If I import only the first 37 channels, and then mark 33 and 34 (Mastoids) when importing, the data is detecting 35 channels and then when I am uploading my Channel location file, that gives the same error message: "The number of data channels (37) including fiducials does not correspond to the initial number of channels, ..."

Also what are your recommendations for Overflow Detection, while importing the data, should it be turned OFF?

Many Thanks again for your help