It depends.
In a WW3 secenario, operating in a kill box for example, the ROE would allow BVR engagements at maximum range. Other scenarios may allow engagement using electronic means of ID.
In more limited scenarios where friendly/neutral aircraft may be in the area, visual ID may be required.
In peacetime scenarios, such as air policing, command authority from the political level may be required.
Nothing, of course, denies a pilot the right to self defence, but he would have to be able to justify it in a court of law afterwards.
Once the ftr has closed beyond the minimum range of a radar missile, he would have to get inside the firing envelope of his IR missile, and older ones, such as AIM-9G etc, were not all aspect. Which probably accounts for getting intoa turning fight at close range at Sidra.