@pharphis - I've often gotten that sense, yes. My logical side tells my it's simply a massive case of
Apophenia, but I can't quite shake the feeling that there's something to it.
The following will apply to spawn locations/densities only, as things like mods on bosses can either almost certainly be attributed to "luck", or straight percentages based on the inherent mods the boss has and the combination of mods he can spawn. Also, as always, bring along a bucket full of salt for this since it is not tested and I am no code master bringing secrets from the depths.
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As
@Neksja suggests, there is a possibility that the pathing you take could factor in to this. We know that pathing affects rack drops, and the infamous
magical line that directly affects Trav spawn locations. Gripp has even mentioned there might be other 'magical lines' for Trav, they just aren't efficient routes so nobody cares. Council members are a hard-coded spawn, sure, but it doesn't seem too far of a leap that there would be some sort of algorithm in the code that has magical lines all over the place that could affect spawn locations of "random" boss packs. Another not-so-far leap would dictate that the magical lines could go so far as to affect whether or not certain boss packs will spawn at all (or rather, if they spawn "out of bounds" - like in a wall, or fiery river - they get dropped, or something along those lines). Maybe this makes sense as to why some maps have such higher densities (check the
Hall of Records if you want examples). Maybe some maps have better layouts of magical lines simply due to topography of the map, giving the map more options of locations to have a successful spawn.
This becomes tricky since we all tend to take a near-exact route on our runs, meaning we *should* hit very similar combinations of magical lines pretty consistently, but it could also mean that when we see these 'trends' of lower density we have subconsciously altered our route in a small way, and once we break that habit and return to our regular route we get back to our 'normal' densities.
I'll just finish this by saying that I don't think this is actually the case. Confirmation bias is a helluva thing, and I'm sure logical fallacies abound in my reasoning above. In a game like this where so much is dependent on RNG the likely explanation is that things are, well, random. However, if someone can figure out a way to test this in a substantial way, I'm all ears.