Stop thinking about the maths and just think about the reality. You have 1 receiver. That means there is a signal coming from the receiver into the processor. There is only one signal. You can't measure it twice and get two different signals.
You may be thinking of the channel matrix, which has dimension 1x4 (not 4x1, sorry). That's because the channel matrix measures the channel from each transmitter to each transceiver. So it measures the way the signal propagates (1) between transmitter 1 and receiver 1, (2) between transmitter 2 and receiver 1, (3) between transmitter 3 and receiver 1, and (4) between transmitter 4 and receiver 1. That is a 1x4 matrix (or vector).