The VRV can be in many locations, even just above the equipment pad. All it has to do is allow air in when under negative pressure so water can drain when the system is off. If it is functioning correctly and sealing (which mine is), the location has no impact on the performance of the system when water is circulating.
In theory putting the VRV at the top minimises the negative pressure in the system when the pump is off and it is draining. But afaik modern rigid panels can easily withstand the negative pressure, so it is a moot point. The manufacturers recommend install location with my system (Heliocol) is at the lowest point of the panels on the supply side, as this ensures the VRV is always under positive pressure and seals correctly when water is flowing.
In theory putting the VRV at the top minimises the negative pressure in the system when the pump is off and it is draining. But afaik modern rigid panels can easily withstand the negative pressure, so it is a moot point. The manufacturers recommend install location with my system (Heliocol) is at the lowest point of the panels on the supply side, as this ensures the VRV is always under positive pressure and seals correctly when water is flowing.