You are right. I made a calculation error previously where I only compared the # of seconds traveling to an ore/gem field instead of total harvest time. They are different because even if gem route distance is 2x the ore distance, actual harvesting time is the same for both fields. This results in a scenario where travel time to a gem field can be 4 times the ore field trip, but because both fields the ore truck needs to stay there to harvest, the TOTAL gem harvest time (leaving Refinery to dumping ore) is only 2 times the ore harvest time. The above is the case for the Allied ore truck on Ridgewar.
In terms of actual numbers, before you were getting 3x the money, for 2x the commute time. So basically you were going out of your base for 50% extra income. Now it's 4x the money, for 2x the commute time, leaving the safety of your base for 100% extra income.