We know that mobs have static total xp values for their level, but based on some old comments (see:
https://www.project1999.com/forums/s...ad.php?t=36484) we also know that the older eqemu code had various xp modifiers applied to that base xp based on the consider color, so it's fair to assume there's likely similar behavior still used for p99.
At higher levels there's a larger range of mobs that will be blue, so a "high blue con" will still give more xp than a "low blue con" simply by nature of the mob having a fixed initial xp value based on its level.
What I'm not sure is if that base/fixed xp is ever enough to make killing a "high blue con" worth it over just slaughtering as many of the lowest possible blue cons you can find.
e.g. (pseudo numbers) if a high blue con gave 5000 xp and a low blue con gave 4000 xp, but you could kill it in half the time, then the obvious win is the low blue con, but if a high blue con gave say 10k xp and a low blue gave 2000, it might be worth chasing the harder blues.
This would also be why some argue slaughtering greens can be better xp, since even after the modifier that reduces the total xp, when averaged over the time it takes to kill them, the greens could come out on top.
If I ever want to know whether a camp or group is efficient or how it stacks up I generally sample how fast the xp moves every 15 to 60 minutes and compare. Just looking purely at the mob level or con or how much your bar moves per kill ignores things like med breaks, respawn times, etc. which are all going to drastically affect your rate.