I'm debating these varieties for planting in my yard on Flying Dragon.

Midknight Valenica
Meyer Lemon
Moro Blood
Trovita Orange

I live in the Phoenix area and my soil is a clay type. What would be the typical mature size for these types? I want a more upright growth pattern and a mature size of 6 to 7 feet would be ideal. Ornamental value is very important as well.

Try Kinkoji for a rootstock instead. It does good in clay as well. You might want to look into that rootstock. It should give you a better form and more vigorious growth than the flying dragon. Its hard to 15F I believe.

I have clay soil also in north Phoenix. I have trees in the ground with C35 and carrizo, which is mostly sold around here. I bought these knowing very little about citrus and wish I did more homework. Luckily they were somewhat cheap.

Sour orange was recommended to me as it is proven in the valley and does better in clay soils. I know it is susceptible to tristeza but the retired grower I talked to said that is what he would still use and didn't seemed worried about tristeza around here. I'm not worried about the size so I'm starting to germinate some seeds.

I'd recommend raised beds if you have clay soil. Here in SE Texas it is 100% clay, you can make red bricks out of the stuff and it sticks to your shovel.

Unfortunately, all my trees are on trifoliate ( FD and C35), save one Volk I believe.

Midknight Valencia would have the largest fruit of the varieties listed.

Flying dragon is great for growing citrus in pots and other areas, but I wouldn't recommend it if you intend to place your tree in the ground. I have a flying dragon tree and have watched it grow 12 inches in 3 years.
Flying Dragon appears to dislike the alkalinity of our soil ,the salt in our water supply, and the 45+ days over 110 degrees every Summer.
Of the many flying dragon trees or edible varieties grafted onto flying dragon I have seen and have discussed with others, they appear to grow 3 inches per year and the tips exhibit a considerable amount of salt burn. As a local rootstock they are hardly satisfactory. I would try trifoliate orange or citranges as a comparison. Perhaps with enough soil preparation to acidify our local soil and deep watering you could get a dwarfing rootstock to thrive.

Patric your certainly correct. Flying Dragon does not do well in high salinity, nor high pH soils. However, Flying Dragon is a Trifoliate Orange variety, and all Trifoliate Orange varieties exhibit the same difficulty when growing in areas of high pH and high salinity. Most all, or all varieties of Citranges also do poorly in salinity and high pH. Cleopatra mandarin, Sun Chu Sha mandarin, Shekwasha mandarin, Sour Orange, Smooth Flat Seville, do a lot better. Volkamer Lemon, Sweet Orange, Rough Lemon do OK. - Millet (1,053-)