My first question is why are you constructing with multiple overlapping layers? If the under layer (s) isn't/aren't critical to the structure or the appearance of the final piece, then the extra thickness... which translates into uneven drying which = uneven shrinkage, is not necessary. I have found that usually a 1/4" - 1/2" overlap for joining slabs is not a problem if the 2 pieces of clay are thoroughly scored and a good slip (with white vinegar as the primary medium... not water (vinegar--- which is a 5% acid solution) will de-flock the clay just enough to get a good bond to set. Drying should be controlled and you seem to have a handle on this aspect of your work. Good luck !