Undercasting Heighten spells

[Zodiac107]

So my question is regarding this. Namely, how does the heighten spell metamagic feat interact with undercasted spells.

My example would be this.
Lvl 12 sorcerer/ psychic
Casts "MIND THRUST"
This is a undercast spell which basically level the spell damage, but lets it stay at the basic spell level.

Now, lets say i apply Heighten spell to "MIND THRUST".

Is it possible in this scenario to max out the damage for that specific spell bracket without increasing the spell slot expended?

For reference
mind thrust
Heighten spell

[Saethori]

You select which tier of the undercast spell you're casting, and then whether you're applying metamagic to it.

You can cast Mind Thrust IV, Heightened Mind Thrust III (by one level), Heightened Mind Thrust II (by two levels), but they all take fourth level spell slots.

Of note is that Heighten Spell doesn't do anything to help you maximize the damage of Mind Thrust, as that's based on caster level, which is static regardless of your spell slot used.

[Zodiac107]

Alright, thanks for the swift answer.

[Vatras]

Applying heighten to an undercast of mind thrust II will cost you a higher slot, but not give you the effects of the higher versions, btw. A heightened mind thrust II is still a mind thrust II, except that it counts as a higher level spell, raising the DC and possibly going through defenses like the globe.
For these spell families heighten doesn't make much sense, as long as there is a version occupying the highest slot.

If you want more damage, you have to go to empower, maximize and intensify.