To add to this....I'll give you a surprising example. My slant 6. Naturally, if something is gonna go against the grain, it'll be something of mine. lol
It is a measured 10.2:1, cranking compression at 175PSI WITH a camshaft that's 250 @.050 with an IVC event of 69*. lol You'd FIGURE it'd take a pretty conservative initial timing setting, right? Wrong. I HAD it at 20* initial and "about" 34* total with the points distributor. I just recently switched to the Mopar electronic ignition that I rebuilt and recurved the distributor for. I welded the governor slots to get 10* mechanical. Turned out perfect. So I put it back on 20* initial and it had right at 10* mechanical for a total of 30*. But I got to playing around with it and bumped it a little more until it stopped idling up and then back down "a tick". Checked it with the light and it's at 23.5* initial. It runs fantastic there. You can tell beyond a shadow of a doubt that's where it wants to be. ZERO spark knock. ZERO kickback on the starter when hot. I would not have fugured it would have taken that hot of an ignition curve, but it did.
I guess what I'm trying to get at is.....like our buddy @MOPAROFFICIAL has preached and preached and preached, don't just "assume" but let the engine tell you where it wants the timing to be. I did, and that's where it runs best.
