I should have said, is there a mathematical way or a study paper that discusses the effect of EMI filter when it is placed after the bridge rectifier (on the DC bus side)?
This isn't for a new design. In the past designs that I have done, I have used a full blown (one or two stage) filter with both common and differential mode chokes before the bridge rectifier. However, I have recently come across some other designs that have used just a common mode choke after the bridge rectifier on the DC bus side (as in the attached figure). Reading more into it, I understand that if the EMI requirements aren't stringent, you can get away by designing a common mode choke that also has an effect on the differential noise. This is done with very wide winding spacing that generates the leakage inductance needed to provide
this differential inductance. However, I am quite sure in these designs that I am looking at, the designer just used a off-the-shelf common mode choke. Which made me think, how can ballpark the filter's effectiveness.