1% for 4 minutes is 100% for 400 minutes, or 6hours and 40 minutes continuous use. You don't have a problem. (You'r also doing the equivalent of calculating your car's mpg after measuring how far you can drive while the fuel guage needle moves a tenth of a milimetre. As am I.).
From Apple's specs:
- Built-in rechargeable lithium-ion battery
- Charging via USB to computer system or power adapter
- Talk time: Up to 7 hours on 3G, up to 14 hours on 2G (GSM)
- Standby time:Up to 300 hours
- Internet use: Up to 6 hours on 3G, up to 10 hours on Wi-Fi
- Video playback: Up to 10 hours
- Audio playback: Up to 40 hours
2G should use less power than 3G, but why cripple your iPhone? I suggest if the phone's battery gets you through the time between when you are able to conveniently charge it, you shouldn't worry about battery usage. If you really insist on judging the battery, do it by timing full to empty, not by timing a 1% drop. Just as you would measure the mpg of a car.
The backlight uses more power than the short communication sessions by the 2G/3G radio. Plus, what you're seeing that's normal.
If you need more power, get one of these, you can fully charge your iPhone 5 times.
You can also follow Apple's suggestions for managing battery life: http://www.apple.com/batteries/ipad.html
The most improvement I have gotten in battery life came when I turned off Push Notifications for all but the most essential apps that I use.