Thank you for your question.
The 375mm to your carpet edge is greater than the minimum 300mm required by Building Regulations.
The 800mm minimum distance to combustibles applies to furniture and soft furnishings etc.
Heat from stoves radiates out and upwards so furniture needs to be further away from the stove, the 300mm hearth rule is to protect carpets and floor coverings from falling ash, coal or firewood when the door is open.
Hope this helps?