I believed in SMAW process, DC electrode negative pole has more penetration in to the base metal because I had read following paragraph in WELDING AND WELDING TECHNOLOGY, McGraw-Hill - PAGE 107

“Two-third of the heat is developed near the positive pole wile the remaining one-third is developed near the negative pole. As a result, an electrode that is connected to the positive pole will burn away approximately 50% faster than one that is connected to the negative pole. This is helpful in obtaining the desired penetration of the base metal.
If the positive ground is used, the penetration will be greater because of the amount of heat energy supplied by the electrode force to the work.”

But, now I have read following sentence in AWS welding handbook Volume 2, Eighth edition, on page 62.

“… Reverse polarity produces deeper penetration, but straight polarity produces a higher electrode melting rate.”

Unfortunately it’s not explained WHY; contrary to McGraw-Hill.