I found the ILA's contract as well, but when I contacted the questioner, he told me he had spoken with someone from the local, and they had answered his question. Interestingly, his answer is different from how pension is calculated in the Master Contract.

Here is what he wrote:
"the ila calculates employeer contributions based on tonnage moved thru a port and/or man hours on the port. tonnage is usually the more lucrative way to calculate the pension. my source in charleston said in his port the pension is based on total man hours on the port ($20 million brought into fund) while in ny/nj they base it on tonnage moved. if charleston were to base theirs on tonnage, the union member said they would take in ($200)."