Flyback smps: Reduce leakage by sandwiching or bifilar winding?

[treez]

Hello,

I am designing a flyback and i wish to reduce leakage.
(both primary and secondary are low voltage)

N(pri) = N(sec)
I(pri) rms ~ I(sec) RMS

Is it best to bifilar wind primary and secondary, or to sandwich wind the secondary between two primary layers?

 

[FvM]

The answer seems obvious. Bifilar windings give the lowest possible leakage inductance. Unfortunately, capacitive coupling is maximized,

 

[szhighstar]

even spread wire across entrie bobbin, reduce dimension of coil.