Yes, who invests first has more chance to make profit with it. But if the scheme only bring few investors everybody is scammed, because there is nothing to be paid. The HYIP owners are always looking for referrals, and referrals of referrals, this way they survive for a bit more time, pay the first investors, share the "it's paying" message and scam all the rest on the end.
HYIP surely is a pyramid scheming scam. Only people on the top will benefit from it with the effort of people on his downlines.
So, downline will work very hard for there money but they don't know only people from the top will benefit from it.