I often get surprised in a skyscraper (I play with random blood without alert) and have no problem with that.
I notice that if these is sleeper in the range at 22pm, they take the place of the bloodmoon zombie.
If you want to skip a bloodmoon, go near a full zombie poi (the crackbook t5 is perfect for that), enter the first room just to make spawn the sleeper (no need to wake up them), as they are about 20-30, they take place of the maxalive bloodmoon. even if they depop, as you do not kill them or not, there will not switch at blood pop as the first one never pop.
(hope you understand what I mean, not english here 
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