Wither rose blocks will always prefer the amplifier an entity has for the wither effect over it's own applied effect. This means that if the player has an amplifier of 0, or 1, they will take damage slower than they normally would when standing inside a wither rose.
Steps to Reproduce:
(optional) Apply regeneration
/effect give @p minecraft:regeneration infinite 255Place down a wither rose, stand inside it
→ observe damage timing intervalGive the player
witherwith an amplifier of 0/effect give @p minecraft:wither infinite 0
Expected Result:
The minimum amplifier applied when standing in the rose would be from the rose itself, and the maximum would be the player's effect applied separate from the rose.
Observed Behavior:
With a lower amplifier applied, the player will be damaged slower than expected.
The wither 1 effect applies damage if its remaining duration in ticks is divisible by 40.
If the entity doesn't already have the wither effect with a higher duration, the wither rose sets the wither duration to 40 ticks every tick, so the entity is tried to be damaged constantly.