slow reply sorry, had to catch up on work and coo over chicks!
8 still doing great with Margaret Hatcher, their silkie surrogate mum.
Ruby I dont think I will be much of a comparison, I'm down to 2 developing eggs. both have stable aircells now not jiggly now, but 1 is very misshaped, comes a long way down the side as well as the egg top.
these were upright for 6 days, with tilting starting after 3, then under Margaret for 3 while the others hatched, then back in incubator and being tilted. i've decided to keep tilting to day 18, mainly to help the chick with the poor air cell move in the shell.
So sorry to hear about your partridge and porcelain.
I was actually wrong. I still have one porcelain egg! I thought the breeder wrote "paint" (it's small cursive writing at the end of the shell) but it's "porc"! That egg is exactly like the one you're describing. I should snap a pic later, as I traced the air cell. It starts in the fat end of the egg but then turns and goes about 3/4 the way down the egg, almost to the pointy end. The dip near the pointy end is loose and it looks like fluid is in there but it could just be the cell jiggling, I guess. I fully plan on intervening if they egg manages to internally pip!! I can work with internal pips. What gets me is when fully formed chicks die without ever getting that far. I really hope you get at least one to hatch, if not both!!

Hatched 5 last month 3 Black, 1 Partridge and 1 White from an overall poor hatch my 1st time incubating only had 8/24 hatch and 1 died at a few days old and my 2 precious Paint silkies dead in their eggs
I set 12 more eggs late July 6 Miniature Paint (micro bantams) from a paint to paint breeding and 6 mixed Silkie Bantam eggs (I'm in the UK we have large fowl Silkies here) possible colours from those eggs are Black, Gold, Paint and Partridge
I'm on day 18 now about to lockdown I have 10 out of 12 left... 1 of the mini paint eggs was infertile and another quit around day 3-4... The aircells in the remaining 4 mini paint eggs are very misshapen so I'm hatching them upright the 6 mixed Silkie eggs have very good aircells so will be hatched laying down getting excited for my eggs hatching now... I'm on the August hatch a long but thought I'd join here too cuz I love Silkies!! 