Your experience of 1.5ppm loss per day was measured with a Taylor K-2006 kit using the 10ml sample size?

If so, the error for each test is at least 0.5ppm (one drop). The measured 1.5ppm loss per day may well have been 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1 all within the test's error margin but painting a different picture of chlorine loss.

I'm sorry to sound stubborn, but, higher FC (at a fixed CYA) loses more chlorine to daily UV than lower FC does.

This may be a reasonable tradeoff and cell life may be limited by other factors (in addition to AmpHour ratings).

If you're more comfortable at a slightly higher FC - Great. If you want to squeeze every last penny, then lower FC is probably cheaper but you are exposed to greater risk from CL usage excursions (think all the neighborhood kids pee in your pool one day when usually only 10% of them do).