You're right on 0.63. I divided a saturated tail by an unsaturated sd. 7.99e-6 / 2.200e-5 = 0.363. The 0.64 is the total bias, and I matched the wrong pair.
On your question: no. Not to 1 percent, and not without your Sigma.
What the second-order term does say, without the number:
Near the fold, d node / d delta is carried by the soft eigenvector v and grows like 1/sqrt(x). A shifted-delta reading is a displacement along v only. Every coordinate then returns the same delta', so the ratio is 1.
The burst displacement is 1/2 J^-1 (H : Sigma). Write it as alpha v + beta u, with u the stiff direction. In delta' units each coordinate c gives
delta'(c) = sqrt(x)/a * (alpha + beta * u_c / v_c)
So the ratio is (alpha + beta u_r/v_r) / (alpha + beta u_d/v_d). If alpha and beta both saturate as the gap closes, it goes to a constant that is not 1, unless beta = 0. That is your 0.968. The formula predicts a limit off 1. It can't predict 0.968 without Sigma and u, and I have neither.
What I can test is how it settles. On your six ratio rows (0.955 to 0.967, fold-1e-9 to fold-1e-12):
fit of 1 - ratio = c0 + c1 x^q limit miss at -1e-10 miss at -1e-12 predicts -1e-13
q free (0.25) 0.970 0.0004 0.0001 0.9687
q = 0.47 (your median exponent) 0.967 0.0015 0.0009 0.9668
So the ratio settles slower than the median does. beta saturates later than alpha, if the picture holds. The two fits split by 0.0019 at fold-1e-13, about six times your per-phase spread. Caveat: four of the six rows are three digits.
Your d4 correction not moving p is the part I'd have worried about. Good that you checked it against the effective fold.
At fold-1e-13, does the median ratio land nearer 0.9687 or 0.9668?