Is that taking into account the clear aperture of the lens?
Lenses usually have 95% CA, or even less for cheaper quality ones.
The outside circumference is not very aspherical and therefore may not contribute to the lux in the spot.
The best way of being sure is putting a circle of paper or metal in front of the lens which has a smaller diameter than the lens, in order to ensure you’re only calculating lux and area for the clear aperture.
OSRAM SYNIOS® P2720, KW DMLQ33.SG White LEDs - ams-osram - ams
Learn more about the compact SYNIOS® P2720 KW DMLQ33.SG LED. Gives you flexiblity and full performance with just one footprint. Fore more information visit the product page.