I have a male dovetail part and trying to make the female dovetail part (screenshot below) slightly larger so movement is reasonably smooth but not too loose. This is for 3D printing of a track for close-up photography. I haven't found anything online so far that addresses this specifically so I've been trying SHELL. That does what I want mostly, but seems to reduce everything when I just need the inner dovetail reduced (lines in blue in the screenshot) to leave the outer dimensions unchanged. 

I drew the female dovetail from a copy of the male dovetail sketch and I have the feeling there's a better way, so any suggestions for any of this are appreciated. 

Thank you