The regs aren't always logical, but we still have to follow them if we want our clients' plans to remain qualified. In this case, the regs make you follow the same rules to reduce a SH contribution mid-year as you would for a complete suspension of the SH mid-year. That may not always seem fair, but that's how the rules work.
I tell clients that going SH is buying your way out of the discrimination testing on deferrals and match. The price you pay is the SH contribution and following the SH regs. And, yes, it can be painful to exit the SH mid-year.