I think by “single gene” they meant not super… heterozygous.
Going back to Travis’ spectrum where BH is -10 and Spider is 10, its likely spotnose is above the 0 mark but not high enough to show on its own.
This is just for a example and doesnt relate to any scientific findings, but think of it like this number line. And lets set the “wobble” mark around 5.
Bh (-10) ------------------- Normal (0) ------ SN,Sable (4) ------------ Champagne (7) ----- Spider,hgw,woma (10)
Like math, 10 + -10 = 0 (Spider + BH)
Spotnose and sable (both 4) dont show wobble, but in their super (8) they do.
Anything over 10 and we are getting into lethal zones (Super Champagne (14), Super Spider, HGW (20)).