Unless I am somehow mistaken, diagonal FlexRamps and DRIs do not exist, meaning ramps branching off diagonal RHWs require deprecated ramp pieces.
EDIT: I got a diagonal A1 to orthogonal MIS to appear by hovering the first piece of the FlexRamp ring over a diagonal RHW-4, but I'm not sure that's the correct one...
EDIT2: Found them both. But they're missing their Euro textures.
I have another problem: Joining orthogonal MIS to diagonal Road tries to pull a tile ID that doesn't exist on the opposite side, like the code was never written with the possibility of such a T-intersection in mind...