Japanese standard: Aichi E13A had a range of 2,100 km, Thats further than all their Carrier based bombers as compairson.
HoI2 standard seem to cut the range in 5 roughly due to return trips and combat exc. So in HoI2 terms such seaplanes from CA/BBs would have around 400km range. 1-3 seazones depending on where you are, probably more in HoI3 since we are promised alot more seazones.
It would be nice if Seaplane scouts and CAGs actually measured the correct range so you could see all seazones they could range from the fleet. Patroll missions should also have all aircraft patrolling seazones in range I hope.