Even if the market falls you will not be able to buy a significant amount of an asset on the exchange without much impact on the price. Therefore, investors participate in ICO.
Certainly, if there is a huge buy wall on any asset in an exchange will automatically affect price positively, in a way, this can only happens if you are investing a very large sum otherwise normal investors can just buy from exchange sometimes lower than ico.
You talk about large amounts of money of what size? At the initial listing, the volume of trading is small and a big influence is exercised by any amount of money.