Hmm, I just tried on a level 32 char and got different results
4315 points of healing, +31 mod, 248 hamp. 20*31*3.48=2157. Pretty sure I'm just doing some silly math, because the numbers I had in my head were the way that rabid calculated it.
What were your melee power and positive spell power numbers when you got 4315 points of healing? Your math 20*31*3.48=2157 looks right to me
if the calc is really supposed to use heroic level without the extra +10 per the wiki article (see next paragraph). You have Light in the Dark for a multiplier based on the higher of melee power or 1/2 (positive) spell power, so if you have about 100 melee power or 300 positive spell power, you would expect to see 2157 raised to about 4315, based on the description.
Normal Lay on Hands: I have a level 4 paladin with +3 CHA bonus from 16 CHA. Zero positive amp. His Lay on Hands heals him from 42 points. The only way that works is if the calculation is (Paladin Level +10) x CHA bonus. (4+10) x 3 = 42.
The calculation for Hands of the Sentinal really looks to be bugged, and treats your level as 10. Light in the Dark is also bugged, at least for me.
I respec'd my Unyielding Sentinal tree to try this with and without Light in the Dark. I'm not getting ANY bonus from it other than AOE.
My L32 character has a CON mod of +27 with positive healing amp 105 and also gets the expected healing based on 20 x 27 x 2.05=1107. However, with Light in the Dark I am still healing for 1107. My positive spell power is 609. I should be getting the heal increased by 7.09/2=3.545X. So it should be 3.545 x 1107 = 3924.
My character is a human wizard who mostly uses negative healing (with neg. amp 241) from all 3 death auras but I've been trying out the Unyielding Sentinal tree for a few weeks to see how I can be more supportive in raids. I can turn undead shroud off and on, and see exactly the 50% healing penalty with it on, so in that case my self heals are only 553. And that stays the same with or without Light in the Dark.