Guys I am all with you in what you said . Even though i was certain that the envelope is related to the likelihood of a successful relight , I went a step further in trying to establish whether the level above the upper limit is a prohibitive one ( in general in such cases the manufacturer tends to be direct by either having a note saying so ) .
Hi,
no, it is just a matter of certification based on the engine manufacturer's data.
More info here :
Turbine Engine Relighting In Flight