Problem with symmetrical bending w/ flex

I have used the flex feature to bend one end of my part (see attached if you wish) as I wanted to. (23 degs)

Now when I want to do the exact same on the other side (mirror feature won't work), the trim planes are not parallel to the surfaces I want to bend anymore. Therefore I don't know what offset to apply to the trim planes so that they act on the surfaces I want to bend (see attached pic).

Can you help me with this?

Thanks.

SolidworksParts And Features