Spell penetration

[hirium]

I decided to improve the spell pen on my toon (20 fvs aasimar in ea) and test it out. After some adjustments I ended up with this list:

• 20 caster level
• 02 spell pen feat (requirement for magister and draconic piercing spellcraft)
• 09 epic destiny: piercing spellcraft (ea, magister, draconic)
• 05 epic destiny: caster level from celestial destiny, ea
• 03 enhancements: aasimar tree
• 01 enhancements: aov tree (no tier5 stuff because i'm using tier5 from beacon of hope)
• 12 gear: nightmother (8equip+4ins)
• 01 gear: sentient (3 piece eye of beholder)
• 09 past lifes
• 01 guild (arcane sanctum)
• ===
• total 63 (+5 on reaper)

then i went in into the mists (non reaper) and tested some spells agains the wisps

• destruction and implosion: show 67 on the dice
• slay living: shows 64 on the dice
• frog: shows 35 on the dice

frog is known to have spell pen issues, but why the difference between destruction and slay living? and what am i missing on the list to justify the 4 difference between 63 (my total) and 67 (in game dice display for destruction and implosion)?