Its 4w/kg averaged over 10g of mass receiving the highest absorption, so if the 10g of tissue near the phone gets 0.04 watts its 4w/kg but only 0.04 joules per second requiring 100 seconds to receive 4 joules.
Cellphone don't put out 4 watts let alone 4 watts per kilogram of a human full human, they might hit 4 watts per kilogram if you are only looking at a small amount of flesh near the phone which is what SAR looks at.
Its like determining CPU performance by looking at perf per watt just because has a high perf per watt does not mean its fast or faster than a much larger CPU.
For instance dancing is around 5 wh/kg for your whole body more than actually getting hit with a tennis ball every second!
Cellphone don't put out 4 watts let alone 4 watts per kilogram of a human full human, they might hit 4 watts per kilogram if you are only looking at a small amount of flesh near the phone which is what SAR looks at.
Its like determining CPU performance by looking at perf per watt just because has a high perf per watt does not mean its fast or faster than a much larger CPU.
For instance dancing is around 5 wh/kg for your whole body more than actually getting hit with a tennis ball every second!