Hi Pyruss, I normally use pair pre-selection OFF, no markers ( I don think they are needed for body scans) and using Masks increases the detail and quality of the results in my case.
Now, if the scan was not too good because the clothes didnt read well, the person was too small so you didnt get enough overlap in some areas, etc. I found that no Mask helps it get the correct alignment easier since it still has the background to use for the calculation.
Just my 2 cents.
Leo