These two statements appear self-contradicting. Could you elaborate what you mean by "twitchy around center"? I interpret it to mean very sensitive to any (small) control input from straight and level flight (relatively unstable). That's the sign of an aft CG, not a forward one which it'd be if nose heavy. With the CG displaced extremely aft, the model may also have a tendency to porpoise which can range from minor oscillations to wildly uncontrollable in the extreme aft CG case. If the CG is excessively forward, the model will be unresponsive to control input and have a delayed response to control input requiring anticipation which can incite PIOs though overcontrolling. To the unfamiliar eye this may be mistaken for porpoising but with larger amplitude and lesser frequency, but is in fact PIO induced. If the CG is way forward, characteristically, loops will be very large.

Although strictly speaking stall is a function of angle of attack, moving the CG aft will predispose the model to more easily exceeding the stalling angle with small control input regardless of control differential -> reduced deflection. If it's heavy as well and you try to tighten up the loops, the wing may dynamically stall as the engine tries to drag the model through the manoeuvre with power. It does sound as if your wing loading is excessively high (heavy model for class/wing area) and this is what is happening.

Me too. That's certainly what it most sounds like as the primary cause, with the CG issue just aggravating the situation.

Models without much wing area and thinner section like SIG's Akromaster and the Baby Flight Streak/Flight Streak Jnr/Mini-Peacemaker fly magnificently in class if you buiild them light, but haven't much leeway for bloat. At that size and area, just a couple of ounces can make the difference between a solid performer and class dog, so you need to take everything into asccount when buildng them from the weight of the wood, through "more epoxy doesn't mean stronger just heavier", white glue is heavy, less is more <performance>, Monokote weighs a lot less than dope and Koverall (even where applied by a skilled hand), and of course, engine weight and fuel tank size. It all counts on a model in this class. As a general rule of thumb, the smaller (capacity) the model, the more critical. OTOH, that's why the Peacemaker and Smousen are better models in class (versus Akromaster or Flite Streak Jnr) with a contemporary Schnuerled .15 even fitted with a silencer. Because they both have a significantly thicker section and 20% more area, they can carry that small (2oz) weight blowout without total loss of performance - ie: turning into an utter dog. Plus they fly slightly slower (higher iinduced drag) allowing more time and ease of increased precision. Hope that all helps. If it's heavy as many fisrt attempt models built when returning to control-line are, then it'll never aerobat well. Put it down to experience and build another.

Sounds like you got it right with the Chippy though! SIG's Super Chipmunk is unquestionably one of the best (& prettiest) sport flying C/L kits out there. Perhaps why it has remained a perennial favourite throughout C/L's twilight?