Not enough topology (vertices, faces) on the source of the target object.
The tops of the object look best when the effect is not as strong.
The meshes need more subdivision.
There are several things to try:
Enable the Gradient Effect to smooth the deformation at the top of the object.
Increase the resolution of the target object by using a subdivision surface modifier.
Increase the resolution of the deformation grid in the Options.
“The bottom of the source object is not pointing towards the target object”
See this video here:
Or follow the explanation below:
The bottom of the source object’s center must be pointing towards the surface of the target object when running the operation. The bottom of the object is the lowest part of the object when the object is not rotated.
You will need to orientate the object correctly by rotating it in Object mode.
The best way to check this is to first visualize it in blender:
With the source object selected, in the top-right of the 3D view, click the ‘Viewport Gizmos’ menu.
Under ‘Object Gizmos’, select ‘Local’ from the drop-down box, and tick the ‘Move’ checkbox. This will display the local X/Y/Z axes for the selected object.
Now, with the object selected, press the R key to rotate it (you can then press X, Y, or Z to restrict the rotation if you wish, and type a number for the number of degrees), and click the left mouse button to complete the rotation. You’ll see that the object’s gizmo axis display has also rotated, as it displays the rotation of the object.
The ‘Bottom’ of an object is the opposite direction of the blue Z-Axis arrow (The -Z axis). It is this opposing direction that needs to be pointing towards the source object.
When the axis is aligned like this, you should now be able to perform the Conform Object operation:
What happens if the bottom of the source object is in the wrong orientation?
You can change the orientation of the axis so that the bottom of your source object is pointing in the right direction:
With the object selected, press the ‘N’ key to access the viewport’s right-hand Properties tabs if they aren’t there already.
Select the ‘Tool’ tab.
Open the ‘Options’ section, and expand the ‘Transform’ tab. Tick the ‘Affect Only: Origins’ checkbox. Now, you can rotate the Origin of the object, and not the object itself.
Make sure the opposite direction of the blue arrow, or in other words the object’s bottom, is in the direction you need by rotating the axes using the R key, optionally followed by the X, Y or Z key to contrain the rotation axis followed by a number for the degrees of the rotation. Press Enter.
When finished, remember to untick the Affect Only: Origins checkbox to go back to normal:
You should now be able to preform the Conform Object operation:
Remember to get in touch if you are having any issues with this.
If trying to use the conformed object as a boolean cutter on the target object, use the Apply Conform Object operation first which will apply all the modifiers - otherwise, Blender will go into a loop where it is trying to use the object to cut, but then the source object itself is trying to deform to the cut shape.
This is an unfortunate effect of Blender’s one-time operation that the settings are applied just once, and the panel is easily lost. You can re-run the operation and the modifiers will be replaced, not re-added. Pressing F9 may bring back the panel, but the settings will not be applied again.