Greetings, all!

If I'm a Sor4/Wizard16, can I take an Air Savant's Improved Heighten Spell enhancement and a Wizard (Archmage)'s Improved Heighten Spell enhancement? Do they stack?

What if I'm a Sorcerer (Air Savant and Fire Savant) and I take the enhancement Improved Heighten Spell from both trees?