I think its a bug, they really wanted to change the supply consumption but changed the firing distance. As you can see:
# 0 - Early Search Radar
model = {
cost = 2
buildtime = 190
manpower = 0.2
surfacedetectioncapability = 1
airdetectioncapability = 1
subdetectioncapability = 0
airdefence = 0
seaattack = 0
convoyattack = 0
subattack = 0
airattack = 0
shorebombardment = 0
distance = 0
supplyconsumption = 0.1
fuelconsumption = 0
upgrade_time_factor = 0.5
upgrade_cost_factor = 1.0
}
# 1 - Late Search Radar
model = {
cost = 2.5
buildtime = 190
manpower = 0.2
surfacedetectioncapability = 2
airdetectioncapability = 2
subdetectioncapability = 0
airdefence = 0
seaattack = 0
convoyattack = 0
subattack = 0
airattack = 0
shorebombardment = 0
distance = 0.2
supplyconsumption = 0
fuelconsumption = 0
upgrade_time_factor = 0.5
upgrade_cost_factor = 1.0
}
Easy to fix though