Judging from your question, you consider HYIP as a clockwork Swiss bank operating within the law. Don't mean to alarm you, but that's not true — almost all HYIPs work on Ponzi scheme principle, where deposits from new investors are used to pay off earlier investors until the whole scheme collapses.
And any HYIP is created not for your enrichment, but primarily to enrich HYIP admin. Therefore, in case of any Bitcoin price fluctuations, most likely, the HYIP payouts will be made at the minimum rate. Moreover, there is always a chance that payouts will not be made at all.
Hey guys, I have 3+ years of HYIP investing. What can I say, if you invest BTC, you get BTC. If you invest PM, you get PM
So if you invest 1btc for 1 month (worth of $6500), in 3 days you get, for example 1.1BTC. No matter, btc/usd rate will be $5000 or $10,000
But again, you should consider investing into HYIPs as serious thing. if you want to earn, remember, as earlier as you jump into this train - possibility of good landing is much more possible