Cool bro!My local hydroponic store is having a rep from foxfarm come speak on cannabis...and free tacos..I just bought these 2x2in gro blocks @420autoflower I was told by @Mañ'O'Green that the 4x4x4in hold to much water...that or you told me..idk I was high....so I went with these....I'll use my seedling tray, heat mat, marshydro control....also a seedling light.....View attachment 1592138
Those will work just fine.
Looks like your small cubes are wrapped so you can either plug up the existing hole in your 4x4x4” blocks with more rockwool and set your 2x2” directly on top, or peal off the paper wrapping around the 2x2” and shave a little off around the edges so it fits in the hole that’s already in the 4x4”