Not sure where you're getting your percentages from.They’ve been running an asset-accumulation masterclass and we’re on the other side of one of them.
Philly MIGHT get as high as 5th in non-lottery draft order which, I think, caps their best odds at 42% of keeping their pick. I think they finish 6th which is 35%.
Going from Tankathon, I get them at 63.9% if they finish 5th worst (possible, though probably not likely). At 6th they'd be at 43.4%. Even if they stay at 7th, they have 34.5% odds of keeping their pick.
You're not calculating as if the pick is top-5 protected rather than top-6, by chance, are you?