Constant polkadot_node_network_protocol::request_response::MAX_PARALLEL_STATEMENT_REQUESTS

pub const MAX_PARALLEL_STATEMENT_REQUESTS: u32 = 3;

We don’t want a slow peer to slow down all the others, at the same time we want to get out the data quickly in full to at least some peers (as this will reduce load on us as they then can start serving the data). So this value is a trade-off. 3 seems to be sensible. So we would need to have 3 slow nodes connected, to delay transfer for others by STATEMENTS_TIMEOUT.