EE Pricing iPhone 5S

These are the pricing plans for EE in the UK for 2GB of data each month. What i don't understand is the 'uneven' price jumps between each storage capacity :
64GB | 4G 2GB | Total Overall Cost For 24 Months = £1,449.75

32GB | 4G 2GB | Overall Cost For 24 Months = £1,368.76

16GB | 4G 2GB | Overall Cost For 24 Months = £999.75

From 16GB - 32GB the price goes up £369.01

From 32 - 64GB the price goes up only £80.99

Shouldn't the jump between storage capacities be £80 like apples pricing?

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p.s I might have gone fully retard here and I'm missing something, but it just doesn't make sense to me that the price hike from the 16-32 Is so high.