Or like you say; if the piston is not at #1 TDC compression.
OP;
The #1TDC compression is the principle player.
The cam could be anywhere, taking the distributor with it and giving an erroneous intake closing point. Everything has to be referenced to #1 TDC compression.
EDIT: you probably know this but on Mopars the #1 cylinder is always the first one on the crank making it the the furthest forward cylinder.