Jaba
Ive never heard the tern light detonation. Detention is the un controlled burn or better explain explosion of the mixture. it either burns or detonates no light heavy. Damage to rods bearing piston heads occur after dentation.
Then you state pre ignition on the engine. Static timing on the TSIO-540 is 20 deg BTDC. The retard points around TDC for starting. You said that pre ignition was 13 BTDC this is after the normal firing point of the magneto. The late the firing once again can cause damage to the valve as the complete consumption of the burn has not had time to be carried, thus a loss of power.
I will add here I have never removed a plug with a broken ceramic in my whole career , omg have I done a lot of plugs in my time.
Im not exactly sure of what you do. You obviously have a high intelligence.
But if I may say lacking a little with hands on in the real word, I don't mean that as a come back or any thing nasty but just what I see on a day to day bases working in the real world get my hands dirty.