Roomy 2-person tarptent using 4 poles?

Adjust your idea slightly. Add netting to your current tarp, but with tieout points that allow you to stake down the netting on the same slope as the tarp instead of the netting coming straight down from the edge of the tarp, so while the 'top' of your shelter would remain the same, the bottom would offer lots more room. Just cozy up and bring the sides in if it's going to rain/if it rains.

Hope that makes sense.

It could be a sort of A-frame with a pair of poles in the center with a spreader bar for shoulder room. The other bars would go at the ends. This should allow side entry.

@Douglas, yeah, that's actually what I had in mind when I said "we could just add netting to the basic ridgeline tarp". We already do use the extra poles to prop up one or two corners (like an awning) if it rains without any wind. It's probably the lightest option.

Just for fun I set up a Squall using 4 poles.
As it is of course is not going to work all that well but if made so that the two rear poles are inside a pocket or just have grommets to sit inside it will work.
Do keep in mind that this is just a quick "mock" set up :

Feeling creative today…I decided to draw up a prototype for fun regardless of whether or not you like the concept.

Tried to think of the most efficient way to make a tent with the least material…here's the single walled tent I came up with that would use 4 trekking poles and most likely weight under 28oz with ease:

For reference, models inside are sized to be 6'0"

If using 1.35oz silnylon for the fly and floor and it being a single walled tent with 4" bathtub (just used 1.35oz for the mesh doors as an estimate) it would come in around 25-26oz before adding tie-outs. 36" tall can comment on it later if you're interested:

@Jordan, that looks interesting. I came up with a similar concept by looking at the Tarptent Stratospire instead of the Squall. Seems like the top might sag but maybe not if I'm careful about using catenary seams.

Overall, though, the Stratospire seems like more surface area than the Squall.

@Franco, the Squall is what got me thinking about doing this. I have the Contrail and really like it and expanding that idea toward the Squall seemed like the logical step.

Actually the top ridge-line that I drew here dips down a little (4in), similar to a Nemo Meta 2P but not nearly as drastically (close to 8in i think)
http://www.nemoequipment.com/nemo2011-meta2p-tent

The concept, is to take a single walled tent like the Meta 2P (just keep referring to that but SMD Haven or Lunar Duo as well as a handful of others are very similar) and shrink it down as much as possible without sacrificing sleeping area. That meant rotating the people 45 degrees and offsetting them slightly but it appears to work.
There's not a whole lot of head room but the sides are pulled out by the 2nd pair of trekking poles so it should help out to make the 36in height feel roomier. This could easily be made larger (42-48in tall) without adding a lot more weight but it just depends on what you want out of it.

For reference, here's the thread I have going on a MYOG 2 person tent:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=66065

I was trying to estimate weights on the one I'm making, which will be quite big for 2 people, and came up with 35oz for a single-walled or 40oz for double walled (detachable, netting/floor) as I haven't quite settled on which I want yet…I'm just working on the fly for now and will figure out the base when I get to it. This is including zippers and but not stakes/poles, thread, or seams and seam sealing…so add another 2-4oz to that and it should be pretty close.

I made it 48" tall now…could easily lower the "wall tieouts" to give it a steeper slope. Here are some pictures to reference what I was thinking at least:

I think the width would need to be shortened slightly if you wanted the walls to be a single piece since it's currently 64" and doesn't allow for making seams where the vestibules connect…would put it closer to 60" to be conservative but the 30" width per person should feel very roomy when laying down.

*** Just to let you know, I'm not at all trying to push this idea onto you. I just love drawing this stuff up so I get a little gung ho about it. ***