The approximate surface area of modern race sails follows a little bit this formula:
Luff size x Real Boom size (you need to add the extra length to the reduced boom size) / 1.4
Floyd, for your sail examples, perhaps not real race sails but I don't care, and I presume no reduced boom length it sums up to:
4.58x1.90/1.4= 6.22 m2
4.70x1.98/1.4= 6.65 m2
So, for sure not 0.2 difference but rather 0.4 difference which is not that far away.
IS87 / IS101 / IS122 / US147