How to keeo missile on the same height of floor ?

[Newdoom]

Hello guys,

I have a fire projectile that spawn on floor when the monster walk, but when is beside a floor that is lower where he walking, the fire fall down the other floor.

How can I prevent that to keep the missile inside the same floor where it spawn ?

ACTOR Fire2
{
//+NOCLIP
+MISSILE
+DROPOFF
DamageType fire
+RANDOMIZE

Gravity 9999
+BloodlessImpact

Scale 1.5
Speed 1
Damage 1
RENDERSTYLE ADD
ALPHA 0.67
ExplosionDamage 3
ExplosionRadius 64
States
{
Spawn:
TNT1 A 8
FRTF A 3 Bright
FRTF A 0 A_Explode
FRTF B 3 Bright
FRTF B 0 A_Explode
FRTF C 3 Bright
FRTF C 0 A_Explode
FRTF C 0
FRTF C 0 A_Jump(191,4)
FRTF C 0 A_CustomMissile("Fire2", 0, 24, 0)
FRTF C 0 A_CustomMissile("Fire2", 0, 0, 0)
FRTF C 0 A_CustomMissile("Fire2", 0, -24, 0)
FRTF DEFGHIJKLMNO 3 Bright
Stop
}
}