4 re 10’s enclosure, 93 s10 blazer

I've been building boxes for years now, but I'm having a problem with the enclosure I built for my blazer, 4-re 10's firing up-ish, kind of angled towards the rear window, but not much, it's loud as I want it to be, but about 30hz or so it falls flat on it's face, I've built about 10 or so boxes for my extended cab s-10, all firing down and they play down to 25 hz or so with no problem, I started at 32 hz on the tuning freq, just re-tuned it today to about 27, with no improvement, it got louder on the higher bass. If I was to build a plate that covers the subs, with about a 3-4 inch gap over them would that help me pick up the lower frequencies? just something for them to resonate off of?

no...what is the net volume and tuning of the enclosure??? I have single Memphis 15 PR in a ported box I built tuned to 40Hz...plays 30Hz no problem.

are they all sharing the same chamber or do they have dividers for each sub? they might be interacting with each other a little bit. just a thought

the enclosure is 2 chambers, very close to 4 cubes after driver and brace displacement, Exactly what re calls for. I thought it was a problem with my ipod, (mentioned in another topic) but i've heard other systems running on ipods and they play the lower notes with no problems. I've always put 4 10's in 6 cubes ported before in the past and they all played deeper than these. Go figure, the first time I use the manufacture's specs I'm not happy. lol. Tomorrow I'm going to give it the poly-fill treatment, if that doesn't cure it I'll just build a bigger box. I want to fire them towards the rear, but my blazer has the inside spare tire, I only have about 28 inches width to work with, and I don't want to double stack the subs to where the box comes above the rear seat.