I think you are referring to realised gains. A trust has no tax...

I think you are referring to realised gains. A trust has no tax liability. Tax is only paid by unitholders.

But I see your point. Let's try to estimate the current realised gains.
So far this FY the only "change in substancial holding" is for MSL. A long term holding which has not done so well.
I guesstimated MAI yet to be realised gains at 13c. For argument sake let's take a conservative approach and say 20c in total.
If you are in a 32.5% tax bracket, your tax liability would be 20c * 50% (CGT discount) * 32.5% = 3.25c.
This would reduce the current discount from 15% to 12.5%.
If you own FOR units in a SMSF in pension mode there won't be any tax so discount remains at 15%.