A question about size function
 

I´m trying to mesh a ducted fan turbovolume using sizing function in Gambit. This works fine but i find that, when i extend the duct domain downstream, the number of volume elements decrease. I mean: if i mesh two ducts using the same size function parameters, the longer duct have the smaller volume elements...i really don´t understant this vehaviour because the comon sense tells me that if I increase the domain size, will increase the total volume elements. Could someone tell me something abuot this???

Thanks in advance!!!

Mike