dso

I have a bit of s side-question to this. I understand SNS and R/T requirements....

But I am looking at R/T fares to Europe in business in October - and I get great one-way business at around $2400 (give or take) when it's at least one week (i.e. leaving Wed, returning Wed. Or any other day). However, if I just take ONE day off that - regardless on what end - the prices in business go to near $4,800 (Y seems to stay the same. Why is that? Is that 'normal' or just a glitch or too far out?
I am, in all cases, staying over the weekend (SNS), but unless it 7 days+, fares are more than double to MUC, FRA (all on UA Metal), TXL and others; while this does NOT happen to CDG, AMS or LHR... It looks like 7 days+ I get P class, while 6 days is Z. That's even though it shows Z9 AND P9 in both cases...