Use different slicer settings in the volume of a selected object.
Example: use a more dense infill in a specified area
per model settings
and select Modify settings for overlaps
.infill mesh only
0
0
0
When you're using Gradual Infill Steps in your main model, don't forget to add Gradual Infill Steps: 0
to the per model settings
Horizontal offset
to a negative number (in mm) to make the model leaner in the horizontal plane. Set it to a positive number to make it fatter. Use small values like for example 0.1mm
.