AWD Addict is right: the RWD/IS "sport suspension" is a completely different suspension package. That means the springs, dampers, bars, etc are all changed. Likely the sport struts have lower spring perches in order to allow for more/better travel, rather than just shortening the spring. Likely the sport struts are shorter, as well.
Go: Cobb S2+, Big Tom FMIC, CP-E DP & DCI, Royal Muffler, AR OC
Turn: TC Kline/Swift SA, Vorshlag Plates, UUC Front Bar, H&R M3 Rear Bar, VAC endlinks & spacers, Forgeline 18x9.5/NT05 265 Square
Stop: Endless MX72, Stoptech Rotors/Lines, Motul RBF600