There is no right or wrong way to do these things, all I can do is tell you what I would do given your situation. As I understand it, you want to sight in at 10 yards in your basement, then be able to take game humanely from 10 to 20 yards. For hunting, I try to set up so that all I have to do is point and shoot at any distance I expect to encounter game (point blank range). For your gun and pellet choice, and
assuming your scope setup is the same as on my R9, if you sight in 1/4" low at 10 yards, you will be within 1/4" from 10 yards to almost 30 yards. Although it would be better if you could just sight in at 25 yards, but as I understand it that is not possible right now. You really should evaluate your own setup using ballistic software of some kind, but this chart gives you the idea of what I am suggesting.
View attachment 102988 I suppose I should mention that to create this chart I did actually enter 25 yards as the zero distance, then just noted where you would have to zero at 10 yards to be on target at 25 yards.