local reactor = data.raw.reactor["micro-nuclear-reactor-1"]

if reactor and reactor.neighbour_connectable then
    reactor.neighbour_connectable.connections = {
        {
            category = "nuclear-reactor",
            location = {
                direction = defines.direction.north,
                position = {0, -0.5}
            },
            neighbour_category = {"nuclear-reactor"}
        },
        {
            category = "nuclear-reactor",
            location = {
                direction = defines.direction.east,
                position = {0.5, 0}
            },
            neighbour_category = {"nuclear-reactor"}
        },
        {
            category = "nuclear-reactor",
            location = {
                direction = defines.direction.south,
                position = {0, 0.5}
            },
            neighbour_category = {"nuclear-reactor"}
        },
        {
            category = "nuclear-reactor",
            location = {
                direction = defines.direction.west,
                position = {-0.5, 0}
            },
            neighbour_category = {"nuclear-reactor"}
        }
    }
end

KI generated, but tested

Thanks for the code, was able to adapt it to fix both mini and micro not receiving the neighbor bonus (which I thought was previously working? But maybe it was only the fusion reactors I had working)

Implemented in v2.1.5