Contagion spread radius feels off

Idk, maybe I'm not correct, but it feels, that spread radius of Contagion is smaller than it should be. Or sometimes it doesn't go off at all, even if enemy is clearly in range. Maybe it can't spread if previous "spread" animation didn't finish?

I tried to compare spread radius with Sigil of Power to get some reference of what it should be and again and again I see this spell doesn't spread when it should.

It does seem to whiff a fair amount of the time