One quick thought on this:
Even though you CAN stack your bique fire packed to max, it is not always a good idea:
Problems that rear their head during glaze fire such as pinholes and bloats, are caused during the bisque fire.
One of the thing that makes these problems is insufficient oxegen presintering in the bisque fire.
When the bisque load is looser the air circulation and oxygenation are improved and thus burn out of organics is more betterer. (;
Not all clays need this but the ones that do, do. Usually it is the darker cone 6 and cone 10 clays that have more stuff to burn out.
All clays would be happy with more air, there is certainly no detriment except what you are doing in 2 loads, you may want to do in 3 loads.
Given that it is usually $15 or less to electric fire 7 feet of bisque, it is a small price to pay to prevent problems and have happier pots and not having to throw out pots with bloats and other issues.