Excessive support when I turn on dual extruder setting

[r111122223333 0]

I'm trying to set up use of dual extrusion with a main material on extruder 1 and a support material on extruder 2, in Cura, for the Ultimaker S5. But the support it wants to generate is ridiculously excessive. In the support settings if I tell it to use extruder 1 (same as model material) for support it generates a pretty sensible pattern under all the overhangs sharper than a given angle. But when I change this single box to tell it to use extruder 2 it generates support all up the outside of the model even where there are no overhanging features to support. It encases almost everything in support for no good reason, I am not considering some ultra slim tower of a model which would risk toppling if not given support all around. How can I stop it doing this and just have support generated, using the second extruder, in the same configuration as it would be in when using a single extruder only.

Thank you

[nallath 1,077]

I assume that you're printing with PVA, which is a tricky material to print right. If the material stays in the nozzle for too long, it can degrade and cause the nozzle to clog. Because of that, we set the "support horizontal expansion" to 3 mm. This ensures that a minimum amount of support is printed every layer, which should prevent this from happening.

It also ensures that the support that it prints doesn't fall over (as is another tendency of PVA).

You can decrease that number for certain models, but it does come at the increased risk of clogged nozzles.