I would always start with the manufacturer's recommendation. Then change it if flights determined it was necessary. But from there I always base mine on flights and not the recommended range. Usually they align, but not always. Unless you fly the same equipment the designer used there will be variations.

Best test I have been shown is to trim the model for level flight. Then do a half roll and angle the plane up to a 45 climb. If it holds the climb with the controls centered/neutral it's balanced. If it falls off it's nose heavy. If it tries to climb it's tail heavy - land immediately and make balance corrections (as it will get worse as the fuel is consumed).

You'll also note that depending on how much fuel you are carrying the model will always be nose heavy compared to the dry balance - unless you've done the pattern fliers trick of mounting the tank at the C.G.. You're adding 10 or 12 ounces of fuel per flight up near the nose.

I like Combatpigg's rule of thumb of no more than two ounces with a 6 pound model. If that don't do it do something else. For tail heavy shim the engine forward on 1/2" Nylon spacers, add a brass prop hub, something. I've even cut and pulled bulkheads back 1" on nose heavy models rather than add excessive tail weight. Lighter always flies better. The advantage to kit builders is you can do a pre-covering balance and get the worst problems figured out while it's easy to make additions or changes.