Normal = 1402 luopan explosion
HP+100% atmas = 2803 luopan explosion
Blaze of Glory Luopan with HP stabalized with Mounted Champion, 713 explosion
Regular Luopan with HP stabalized with Mounted Champion, 1402 explosion
Luopan with Mounted Champion, 23 HP Life Cycle
Luopan with Mounted Champion and Stronghold, 23 HP Life Cycle
Luopan with Mounted Champion and Stronghold w/ Lasting Emination, 17 HP Life Cycle
Luopan with Mounted Champion and Stronghold w/ Lasting Emination, 1408 explosion
Luopan with Mounted Champion and Stronghold w/ Ecliptic Attrition, 28 HP Life Cycle
Luopan with Mounted Champion and Stronghold w/ Ecliptic Attrition, 1397 explosion
My tests suggest that a Luopan has 1425hp at Lv99. For some reason, Luopan starts with and maxes out at 3 less HP than its initial expected DoT tick. I have summoned Luopans at full HP or half HP with mounted champion and allowed them to sit for over a minute while checking pethpp to find that the HP neither increases nor decreases which suggests that the DoT effect is being perfectly canceled (i.e. is 20hp/tic). I have also done life cycle 2 times in a row with a revitalizer for 23hp meaning that the initial decrease in HP does not correct itself. The Blaze of Glory Luopan test resulted in a 713 explosion which is about half of 1425, but off by 1 likely due to rounding or the steps taken to decide its HP in the code.
The above changes in life cycle or concentric pulse damage confirm the suspected DoT rates.
Normal Luopan = 20hp/tic
Lasting Emination = 14hp/tic (6hp difference in life cycle and concentric pulse when used)
Ecliptic Attrition = 25hp/tic (5hp difference in concentric pulse when used)
My tests suggest that Luopan decay rate is decided at the time of summon. With HP+100%, I noticed that the luopan lasted the normal amount of time rather than double which one might initially expect.
Theory:
Normal DoT = MaxHP / 70
Lasting Emination = MaxHP / 100
Ecliptic Attrition = MaxHP / 57
I found that DoT does not react to changes in HP once the Luopan is out. If I summon a Luopan with only Mounted Champion active, then add Sanguine Scythe (HP+20%), its HP remains the same when checked with pethpp. I used this to further confirm Luopan's HP. Luopan summoned with only Mounted Champion active should start at 1402 / 1425 hp. With Sanguine Scythe added, the max HP should become 1425 x 1.2 = 1710. Life Cycle used after Sanguine Scythe should restore 308 hp which is what happened.
Conclusion:
As far as I can tell, Luopans explode for exactly their HP in damage. However, for some reason, the initial HP when summoned does not match the first DoT tic exactly. A standard Lv99 Luopan has 1425hp.