1. That flexi is kinked, and will eventually fail, never mind any flow restriction.
2. Possibly as the hot water flows, the copper pipe expands length ways and further kinks the flexi, reducing the flow.
3. You need to replace the flexi, like for like, and adjust the length of the copper pipework to make it fit without kinking. When you do, get rid of the PTFE. The seal is between the rubber washer in the end of the flexi and the (hopefully) flat rim of the taps' threaded shank.
4. While you are at it, I'd check the cold to make sure you haven't got a similar problem.
2. Possibly as the hot water flows, the copper pipe expands length ways and further kinks the flexi, reducing the flow.
3. You need to replace the flexi, like for like, and adjust the length of the copper pipework to make it fit without kinking. When you do, get rid of the PTFE. The seal is between the rubber washer in the end of the flexi and the (hopefully) flat rim of the taps' threaded shank.
4. While you are at it, I'd check the cold to make sure you haven't got a similar problem.