Wool Pile without center fin?

I have installed your wool pile 58-022 size 9/32 x 9/32 in my double hung windows. While the windows open and close, they are tight. Tight to the point where they will stay in any position without the use of a window balance. I believe the 9/32 x 9/32 is too big and is the cause of the tightness.

I see that you have a wool pile 58-045 size 9/32 x 1/4 but includes a center fin. I think the center fin would work on the horizontal tracks but not on the vertical tracks, could be wrong, but I believe this size would eliminate the tightness if not for the center fin. So my question is the 9/32 x 1/4 available without the center fin, and what is your take on the center fin on the vertical tracks?

Thanks
Isadore