I can understand the trepidation of trusting a calculator but maybe can help lay it to rest. Last winter I designed & built a 35cc model and used the calculator for the CG. It nailed the position. I've played both fore and aft and came back to the position, which provided a neutral elevator, no pitch coupling in knife edge and common power on/off trim.

btw... 4.3" is a good number for the Seagull Spacewalker II 1.20. Upgraded recently to LiFe batteries and rebalanced and flew mine last week and it flew great with that number.