The "25-35% of the MAC" figure is just a starting point for estimating the center of lift for that one surface.
If you go back to those calculators, make a test by increasing the size of the horizontal stabilizer (the tail) to the same as the wing. You'll see the CG has probably shifted completely off the wing to some point behind it, which is where it really would be if you made a plane like that.
I would probably go back to http://adamone.rchomepage.com/cg_calc.htm and make 2 more calcs, one with a 5% margin and the other with a 15% margin. Those measurements would give you the minimum and maximum bounds for the CG of that plane, and I'd probably start somewhere between them, at 4.99" from the LE.