Questions about landing area

[Zimmy]

I'm laying out the floor of my 42" oven build and have some questions:
1. How important is the landing area depth dimension (not thickness)? The Pompeii plans call for an 8" vent landing and a 12" oven landing depth. I am a bit constrained on oven depth in my corner build due to where I poured the 4" thick x 42" diameter area of vermicucrete. I can get maybe 7-8 inches of oven landing before I am at the edge of the slab. I see some build photos on here that seem to have almost no landing, although they do appear abrupt/truncated. My L-shaped setup has a prep counter on one side and a bar on the other to place items coming out of the oven, so if it is just for a convenient resting spot I am fine to lose a bit of that feature to the front.
2. More about landing geometry: I see several folks have made a T-shaped landing with their floor where the vent landing is narrower than the oven landing, presumably to create the reveal that allows an inner door seal. I plan to build a brick dome arch a la Mongo's 42" build thread so I think that means the narrow part of the T is one brick length (9") deep and then widening a bit for the decorative external arch. Does this butt up against the dome arch, or is the flue opening a third arch? A top-down view of the footprint of these features would be really helpful.
3. What, if any, clearance is needed between the floor bricks (trimmed to 42" diameter circle) and the dome bricks? I plan to just butt them up against each other while laying the first course.
4. I hear some clearance between the dome arch and the decorative arch is good to accommodate thermal expansion. What kind of gap are we talking 1/8", 1/2"? Does that gap then get covered with the exterior finish?
I'll try to get a build progress post up here soon.

[JRPizza]

Hey Zimmy, I also did a corner build so you might want to take a look at my build thread. I learned, like you are, that fitting an oven into a corner is more difficult than it looks!
I am somewhat confused by the terms vent landing and oven landing, as many ovens, including mine, have the oven set so the vent landing is close to flush with the front of the slab and there is no additional landing. I missed being flush by the width of one brick thinking I might add a decorative layer to my arch, but decided I didn't need one. I guess you could extend the area if front of the oven increasing the length of the landing, but too much makes it harder to maintain your fire and cook your food.
Your minimum landing (vent) will be determined by what kind of vent you build. A common length for brick vents is 1.5 bricks, which gives you a good structure and plenty of room to transition to your chimney. Some folks use a cast or pre-fabbed metal vent that allows for a more shallow landing. You need to plan out what your chimney will look like and how you want to attach it before you know exactly what your landing length will be.

[JRPizza]

Regarding your second question, my "landing" does have two widths - there is the initial width that sits under the inner arch, where the inner arch controls the oven opening width, and a wider longer vent floor that sits under the chimney and exposes an inch or so of the inner arch for my door to seat against (the reveal). In my last post I said the vent landing is a function of the construction type and design of the vent, but there is also a few inches you can play with depending on how fore/aft your inner arch sits in relation to the oven dome. Have a look at my build and see if any of this makes sense.

[Zimmy]

Appreciate the response JR. That makes perfect sense. Since I do seem to be more constrained on depth than I expected, I plan to have part of the cutout for the vent in the dome arch and the bulk in the slightly larger vent arch so I can get away with one course of 9" firebricks for each and then I might be able to squeeze in a shallow arch of decorative bricks in front of that to protect the fire bricks and to have a reveal for the blankets/stucco to butt against. Slightly reducing the diameter from 42" to 40" is in play as well. One thing that is giving me pause is having the vent span the dome arch to the vent arch mechanically couples them, which seems to be the opposite of what folks are doing to isolate them both thermally and mechanically. Maybe slotted holes in the DuraVent plate with Belville washers will allow some movement.