So I spoke to CS..

They said not eligible for Dubai connect since there are other flight combinations with lesser transit time available ( EK573 / EK133).. so even though EK131 is the earliest outward connection post EK571 reaching DXB and there is also no other feeder connection from CCU reaching DXB before EK131 departs, they cannot offer Dubai connect facility.

Basically this means that if EK has 2-3 flights a day from some place, even if one of the onward connections from DXB is less than 8 hrs (Y), no eligibility for Dubai Connect !