Trouble editing metaball

Hi ,

I am currently doing my final year project and i have trouble with editing metaball. as metaball merge all balls together, i do not know to control it. i am trying to achieve a metaball skin but i do not want the middle part to be merge together as i want that part to be hollow. the image label (1) is my interior space with the middle circle being hollow.

attached is the metaball grasshopper im working with , i can’t seem to make the middle hollow. (10.4 KB)

One way is to make interior volume separately and subtract it(solid difference) from your metaball shape.