Since HashFast states prices in fiat (and other miners, I still don't see why reinvest only has to be HashFast), why wouldn't a rising BTC simply give more hash rate to IceDrill?
Because most existing funds were already paid to Hashfast - so any gain from the increase in price of BTC gos to Hashfast not Icedrill. That was always clear from day 1 - it's not something that should be surprising.
Dates were always published when payments would be made to Hashfast - and the funds raised so far (less those held back for infrastructure) were paid in August. I know that - and I don't even have any special interest in this security (it's just one of many that I trade).