20% will not suffice. Unlike „ordinary“ Home Bias, the CHF is a safe harbour currency and Swiss shares have a heavy weight on conservative Sectors. This implies a certain downward hedge. As long as you re-balance, Swiss Shares will help you to sustain a crash.
In between Crashes, we still have the situation that Swiss shares beat the NSCI World. Dont ask me why, this might be a matter if the polutical stability we experience here? So they are not only an investment in bad times but simply anytime.
In addition to this, unlike foreign shares you neither lose in explicit nor implicit FX cost and there is zero Withholding Tax loss. This in my view justifies about 25 to 30% if Swiss Shares.
Same applies for hedging, its generally a bad idea but given the nature of the Swissie as a safe harbour currency, it actually as well pays off to hold a certain amount of global shares with a CHF hedge. Know that doesnt quite sound logical but empirically, there is Value. BUT if you hold FX hedged Shares you should re-balance at least quarterly if not Monthly. If you can do so, it may as well make sense to hedge about 5 to max 10% of your Shares.
So how about 25-30% Swiss Shares, 5 to 10% Hedged and the Rest just Global shares?