Was struggling with the builds out there (maybe I'm too low stats), but was bascially getting pwn'd any time my tower boost monk would go on cooldown, so spent some time to come up with a more stable build. 

I've run this build a solid 20-30 times, and it's great.

We take advantage of the high ground on the east side of the crystals.  This enables us to cover both upper and lower crystal with seed bomb towers.

Auras as shown. 

Reflective beams are north, south, and west of the build.

Minions act as physical wall blocking access to the tower stack.  Nothing gets close except from the Southeast side. Minions are just keeping enemies from walking onto the build, you can use any mix of minions you like to close it off.

4 party members, Tower Boost Monk and 3 Summoners with Guardians.  Tower Boost the whole time.  On first wave I swap one of the summoners for an Adept upgrader and get the whole stack to 3 stars (usually right as the wave ends everything is 3 star), then swap it back out for the 3rd summoner to run the rest of the waves.  I like Ruthless for Jester Guardian farming because the quality of the rolls are much better.  I've even gotten 4 Ult rolls from a single Ruthless run.  The downside is it takes more time.  You could probably run 2 or 3 NM runs in the same time.  But after many, many,many NM runs with very poor rolls, this is where I'm at.

Hint 1: 5 Seed bomb towers, near the edge, but not outside the reflector beam, facing 2x Noth West, 2x West, and South West

Hint 2: 3 DSTs, facing northwest, southwest, and southeast; 4 LTs and a Mushroom and a Golem and Nature Pylon.  Keep everything inside the reflector beams and stack as tight as you can and get everything onto a small buff beam.

Hint 4: Gas Trap on the lower floor NW of the crystal

Please let me know if it works for you.  Happy hunting those elusive Jester Guardians (still haven't seen a Tier 6 roll for me)