hindsight views on layout for 42" oven wanted

[semlin]

hi folks, i poured the top of my hearth yesterday so i need to lay out the insulating layer now and i am getting serious about design even as i keep reading this site and learning more. pretty much the only thing set "in brick" in my mind is a 42" dimension dome with a 21" ceiling. i will be intersecting the arch with the oven wall giannifoccacia style (with apologies to others who also originated it).

i would very much like to hear the voices of experience on the following design elements to help me make some final layout decisions. i am also looking for good links as i keep finding stuff on this site that changes my approach!

1. what depth is best for the exposed outside landing shelf beyond the oven? (distance between outer oven arch opening and outer edge of hearth structure including any overhand). i was originally thinking 12" to be able to place a pizza there but now i think it maybe should be less to allow easier access to deep into the oven.

2. what depth of vestibule works best (distance from the outer edge of the integrated oven arch to the opening of the outer arch)? again, i am thinking as short as possible with a doubled half brick arch at the entrance and a single half brick arch offset against the dome arch at the other, and then only exactly enough depth between for the flue. is that right? also, if there is a definitive flue design thread i have not found it yet. so far i like what alex dum/it guy did but i am not sure i can reproduce it.

3. i understand arch height, but what width of opening for the oven arch has worked for people? should i go wide so i can so i can get bigger pizzas in the oven?

4. i have seen (i think) comments about tapering the vestibule outward from the arch. not sure if i am missing something if i just run it straight out?

[semlin]

i asked too many questions. apologies. here is a hopefully more focused question.

can i make the flue initially narrower than the pipe diameter i plan to use? for a 40" oven, i am thinking of a 20 wide x 6" deep flue chamber that narrows on width but steps out on depth as it rises to allow fitment of an 8" pipe.

does the answer change at all if i choose to finish it as a squirrel tail chimney with an 8" flexible liner? i am thinking about this.

BACKGROUND

after some layout attempts on the hearth i have realized i overdid the corner cutaway on my hearth and i am now space challenged and involuntarily downsizing from 42 to 40. even that is tight.

assuming i build a 40" dome with a 20" dome arch opening 12.5" i think i need an 8" chimney pipe?

i can fit a 40" inner diameter oven on my slab (allowing 8" for firebrick thickness, blanket and mortar), and yielding 16" remaining for the vestibule with a 1.25 inch dome arch protrusion.

if i assume a 4" reveal arch with a 1.25" inch "L" shape overlap for the heat break and 1/4" ceramic rope (3.00" net depth) that leaves me only 13" for the flue depth, outer flue arch and decorative arch.