I run the Z12 system on a 3200 USD account with margin 30 and risk 10.
It has never opened any indicies. In log it says

NAS100 Skipped Margin 14 min 49
GER30 Skipped Margin 8 min 113

Broker has minimum 1 lot and 1 lot steps for indicies

Is there any way to allow these trades, but not over expose currency pairs. Account has 1:888 leverage on forex, but 1:100 on indicies

This is from my AssetsFix file

GER30,10734.50,2.0000,-0.7800,-1.0000,0.0100,0.010000,114.0400,94.129,1.0,0.000,GER30Cash
NAS100,4871.45,2.0000,-0.4700,-0.3300,0.0100,0.010000,48.7100,100.009,1.0,0.000,US100Cash

Maybe your broker doesn't allow mini lots for indices.and full lots take too much of your margine.

Yes, xm.com has minimum size 1 contract and at leverage 100 that is 49 usd for NAS100
But 49 is ok by me. Zorro wanted to open a NAS100 that required only 8 usd margin and that is not possible if minimum is 49. I wondered if there is a workaround to let it open the trade anyway.

Well, you would need to increase the margin slider for that, but that will increase the risk as well.

Could this be a problem since it is such a big differance between margin requirements on forex and on indicies.
I mean, forex it is leverage 888 and on indicied it is 100.
But if I request a change of leverage to 200 or even 100, then forex would be 200 (or 100) and indicies still/also 100.

Because if I increase margin slider, it will affect forex trades 8 fold, and that might not be optimal.

Or is the problem that Zorro wants to open smaller contracts then the broker provides?

No problem with Zorro. Your first point is correct. If your broker does not offer mini lots on indices, don't trade them, or change your broker, or trade them separately on another instance of Zorro (Zorro S).