I think peaky a d spike - triangle in a square - units work out better when the pieces are cut to suze.
I think I cut accurately a d when piecing squares and rectangles.- using my 1/= inch seam - the units end up being the size expected.
For reasons I do not understand, I need to make the seams narrower when sewing triangles to get the unit to be large enough..
I usually do a practice piece before proceeding so I can make adjustments as needed.