using 4x4 (and higher order) MIMO offers some features which give better service outside best area of AP coverage (beam forming, space diversity). The power backoff explains why maximum throughput can be same on two APs with different signal strengths, specially if Tx power is set for maximum coverage area. In case of PtP links, using higher fain antennae on both ends help improve both directions. However higher gain antenna helps in uplink, upload will be better because AP 'hears better'. If country regulations limit Tx power lower than PA capability, then real power backoff happens at higher VHT or even doesn't happen). When using higher gain antenna on AP downlink doesn't change much (if at all): coverage is the same, service is the same (or slightly better power amplifiers in low cost WiFi APs have 'power backoff' meaning that when transmitting higher MCS/VHT, the power capability is lower. Higher gain antenna, by being directional (more or less), can also help to reduce noise part of SINR, but amount of reduction highly depends on overall situation around receiver. Sum of first two is more or less EIRP and thus limited by country regulation, path loss is property of physical space between transmitter and receiver and receiver antenna gain is something that can be improved on certain devices. Signal in receiver is sum of transmitter power (power amplifier), transmitter antenna gain, path loss and receiver antenna gain. Remember that obtainable throughput is related to SINR of receiver. higher gain antenna does help to improve reception. So for best coverage use 1-chain AP with 20MHz channel width. With wider channels power is dispersed more and signal strength will again be lower. It will also mean that it will sum power per whole channel width. 4x4 MIMO or higher) will present as lower signal strength. Per device means that it'll sum over all transmit antennae and using many antennae (e.g. Effective means it takes into account antenna gain so high antenna gain on transmitter will not present as higher signal strength. What country regulations limit is effective radiated power per device.

Hap ac2 routeros 7