Personally, I feel it is a bit unfair, even if it's only a split second of the mark, you should have chance to defend yourself.
I know recon doesn't see a whole bunch of use due to it being very punishing, strikers having more utility, and a variety of other reasons, but these should not be offset by unbalanced and unfair game mechanics.
I think you should get the warning the moment you enter a recon's radius and still have the pulse to bring about the death mark, but increase the pulse's speed to help offset the earlier warning.
Is it fair that snarble/flourishes are annoying or there is no pure pierce defence?