You do not have Full Range capabilities.
Your JBL "bass Cabinets" are rated as "usable" down to 35Hz.
Those Peavy 118s are rated F3 @ 40Hz.
You are using Pro Gear for HT, which is fine, but the actual performance specs do not line up with what is expected for HT Gear in terms of what the necessary FR is for the different parts of the mix.
LFE Content goes down as low as 3Hz, up to 120Hz. A proper Full Range speaker should produce 20Hz-20,000Hz, ideally ±3dB. Most modern Subwoofers will cover anywhere from 15-18Hz on the low end, up to 150-200Hz on the high end.
The proper setting is in fact "SMALL" for the Speakers you detailed. I don't know what you are using up high, but down low... you are coming up short, I'm afraid.