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Depending on the length of your corrugated hose, the placement of the nipple on it, the location of the tank valve under your arm, your body size, and the kind of first stage with its various ports, you may need a different length LPI hose to avoid loops and tugging.
First stages with a fifth port make the inflator hose routing nicer. On my SM rig, my corrugated hose comes from lower left corner of wing across my torso and is clipped to right shoulder D ring. This is cave style so the elbow is protected from being mashed on cave roof. LP hose comes from fifth port on left tank first stage.
The lpi hose length is usually about 9 inches, sometimes a little shorter. The lie pressure inflator is bungeed to the area of the left or right chest d-ring. The lpi just had to be long enough to go from the armpit to about the center of the chest.
Sidemount often uses a very short regulator inflator-hose (about 9 inches) for inflating the BCD. The tank-valve is closer to chest level. The "ideal" configuration uses a low-pressure port on the end/center of the low pressure swivel turret on the 1st stage. SM BCDs also often have the BCD-inflator-hose starting from right above your butt, running up the side, and towards your chest. You can also do over-the-shoulder, or use the shoulder-port, but route under your arm, but that's less common.
