If I put a 16 followed by 2 12s and plug in 2 heated buckets and 2 250w heat lamps the lamps will dim but if I reverse it and put the 16 last the lamps will not dim when everything is plugged in because the first 2 cords get more power to the last one than the smaller cord could get to the other 2 if reversed.
No, it really doesn't work that way. If you saw that in actual practice it was not because of the order of cords, but because of a bad connection someplace that was corrected when you swapped the cords around.
You can model the three cords as three resistances in series going to the load, and three resistances in series completing the circuit back to the power supply. It doesn't matter what order you put the resistances in, the sum of the resistances is always the same and the sum of the resulting voltage drops is always the same. You cannot reduce the total voltage drop by rearranging the cords.