There are easy and hard bosses.
For boss level 20-60 there are only easy bosses with power = level * 10,000 - 100,000

Easy bosses with level 60-99, Have power = level * 10,000 - 100,000
Hard bosses with level 60-99, Have power = level * 10,000 + 900,000

Easy bosses with level over 100, Have power = level * 10,000 - 100,000
Hard bosses with level over 100, Have power = level * 10,000 + 7,700,000

The level of the bosses you summon are alwasy between half your boss kill Count and your boss kill Count.

So a level 100 boss can have eigher have 900,000 power or 8,700,000 power.
and a level 60 boss can have eigher have 500,000 power or 1,500,000 power.
I seem to get the hard bosses type atleast 95% of the times atm.
I would like to see chance of hard boss not going over 50%.

So a player with kill Count 200 summon bosses with level 100 to 200, but as bosses 100+ have 95%+ chance of beeing hard so al least 95% of the bosses he summens will have of power 8,7 M or more.

Well that explains a lot. And 95%? Try my 100%. Admitedly i guess i can't complain, at the moment i have exactly 700 kills

I agree, there could be a smaller chance to get hard bosses. Maybe i'm just extremely unlucky, though. Always felt luck based systems like this type could use a counter with "if you get X many hard bosses in a row, your next boss will be an easy one."

[MENTION=101]ChibiKika[/MENTION]
I agree that paying players should have an advantage since there isn't really a lot of other things you can buy with money. I'll never be wanting to pay the sums they do, and all the more power to them if they want to support this game and get the higher ranks for it, since us free players can still get a lot of bang for our unexisting bucks.

I have voiced my opinion about exclusives before though, but that is another matter

Glad to see the opinion of a paying player, having words from both sides helps to see the subject with a broader perspective.
Every game needs to generate an income stream, so I pretty much agree with the current advantages that cash spenders receive, since IMO those advantages aren't game-breaking as tends to happen in other games.
More than that, the current situation of F2P players forced us to plan our gameplay better and organize, which I loved xD yet I still resent not being able to get the only 2 event cards I actually wanted.

Regarding the bosses situation, I pretty much spent the entire event helping as much friends as possible, and I found it quite fun. I tried to land as many full-energy attacks as possible, so the only situation that complicated me was when many bosses spawned at the same time, 'cause it forced me to provide weaker help with 1-energy attacks each. My group raids idea pretty much aimed to provide a more coordinated way for every community's members to provide help to each other as effective as possible, and of course, to (everyone) have a better shot against those 8.7m bosses bug.

And speaking of that, I just don't buy that Nutaku planned the 8.7m guards thing.
The fact that they acknowledged the complains about what happened, plus their announcement of revision and compensation (why would they ever have to "compensate" us for something working normally? they realized something went wrong!), plus the japanese wiki's HP scaling for bosses showing the actual expected HP scaling, makes me think that Nutaku didn't planned that 8.7m guards situation from the beginning, but they likely realized a potential extra income flow in that bug, so they left it like that. In theory.
Either that or the actual solution of the bug wasn't under their technical possibilities. That would be understandable, actually.

Just my humble opinion.

Remember, Nutaku doesn't have any ability to modify the code. That's completely in the hands of DMM.

Nutaku has stated that they have a lot more control over peropero than Aigis. The way Nordland was talking sounded like they modified the boss HP code themselves. Not that I can confirm that.