SPF lower active content with higher rating – how is this possible?

Hi all

I think I have found the most perfect SPF for me, its mineral based, its inexpensive, non greasy and actually improves my skins appearance! It has a rating of SPF 50 yet it only has Titanium Dioxide 4% and Zinc Oxide 4%

Australian Gold Bontical Tinted Face Sunscreen:
Alumina, Butyrospermum Parkii (Shea) Butter, Caprylyl Glycol, Cetyl PEG/PPG-10/1 Dimethicone, Cyclopentasiloxane, Dimethicone Crosspolymer, Disodium EDTA, Disteardimonium Hectorite, Eucalyptus Globulus Leaf Extract, Glycerin, Hexyl Laurate, Iron Oxides, Panthenol, PEG-10 Dimethicone, Phenoxyethanol, Polyglyceryl-4 Isostearate, Polymethylsilsesquioxane, Porphyra Umbilicalis Extract, Silica, Squalane, Stearic Acid, Terminalia Ferdinandiana (Kakadu Plum) Fruit Extract, Tocopheryl Acetate, Triethoxycaprylylsilane, water

My confusion is that the product I have been using till now only has an SPF rating of 25 yet it has a much higher ACTIVE INGREDIENT content ZINC OXIDE 7.3%, TITANIUM DIOXIDE 6.9%

Clinique City Block Sheer Oil Free Daily Face Protector Broad Spectrum 25 SPF:
Active: Titanium Dioxide (7.3%), Zinc Oxide (6.9%), Other: Water, Trioctyldodecyl Citrate, Butylene Glycol, Cyclopentasiloxane, Dimethicone, C12-15 Alkyl Benzoate, Steareth-2, Stearyl Heptanoate, Silica, Lecithin, Ammonium Acryloyldimethyltaurate/VP Copolymer, Gentiana Lutea (Gentian) Root Extract, Rosmarinus Officinalis (Rosemary) Leaf Extract, Hordeum Vulgare (Barley) Extract, Betula Alba (Birch) Bark Extract, Cucumis Sativus (Cucumber) Fruit Extract, Laminaria Saccharina Extract, Saccharomyces Lysate Extract, Helianthus Annuus (Sunflower) Seedcake, Sodium Hyaluronate, Sorbitan Tristearate, Linoleic Acid, Polyquaternium-51, Caprylyl Methicone, Sorbitol, Sodium RNA, PEG-40 Stearate, Caprylyl Glycol, Tocopheryl Acetate, Phytantriol, Stearic Acid, Hydrogenated Lecithin, Cellulose, Magnesium Ascorbyl Phosphate, Stearyl Dimethicone, Ascorbyl Tocopheryl Maleate, Nordihydroguaiaretic Acid, Linolenic Acid, Pantethine, Bisabolol, Ceteth-2, PEG/PPG-18/18 Dimethicone, Polyglyceryl-6 Polyricinoleate, Steareth-20, Isopropyl Titanium Triisostearate, Propylene Glycol Dicaprate, Sodium Stearate, Nylon-12, Citric Acid, Aluminum Hydroxide, Nylon-6, Hexylene Glycol, Xanthan Gum, Disodium EDTA, BHT, Phenoxyethanol, Titanium Dioxide, Iron Oxides

Looking forward to your opinions on these two products and if anyone can enlighten me on how the rating can be higher with lower active ingredient content I would really really appreciate it!