Sigh! PLAYERS! USE Combat item TRICKS, Trips, Line of sight Obstruction or melee Feints (If In 4e) first to reduce Chances of any OA Melee hit!, then try next round your Acrobatic "Glory movement" Trick.
Forward momentum and natural Size mobility class change effect to your own body to small size. Dive forward, The "Tuck and Roll" on the floor under their or around there legs (be it between or on the outside of their legs, Ascetic's of story telling for movement) Action Example: A Highway motor cycle Cuts the Yellow line between 2 cars or semi-trucks. Same concept basics.
OR Use your stationary "jump/'sault" momentum to "CART-Wheel" Over their Lowered Weapon, or the side farthest from, as a pass thru Square acrobatics. I suggest Anything 4e Legal, to lower their Hit chances and likely OA odds. Kicks (armed generic OA's) from an adjacent foe means a balance fail & down on hands/back prone.
Contrast AN Effect Equal to this likely Is Acrobatic also do to Spinning Dizziness Factors & (lack of)resistances: A Monks "slide of" Block, spin step forward, Block, spin stride move through their hex/square by Close-est of Close-Combat into their standing body space (stepping behind their forwarded leg with his own ect.) to arrive behind them or THE leg grapple at Hips-jump and bend sliding between obstacles legs arch. Or acrobatic hands dive past obsticals side and low hand-stand kick into roll unto non-prone footing.
Somersault Requires Strong up-jump momentum + Acrobatics skills to Execute. Action implies a Top Over jump-Dive while Executing one forward head-over legs flip stick the landing behind the foe for a "pass-thru". I'd rather not fall from Height (at perhaps half dmg for 5-6 foot falls) and get multi OA hit while flat-back & winded this and next round.
Edit-addon AN OVER THE TOP OF AN OBSTACLE"S SOMERSAULT A Jump utilizing LEVER Physics as one prime part of success, including both hands (or 1 or more sword held fists knuckles down, or 2 empty Hands) on the "Obstacle's/Foe's" TOP Parts or Shoulders AS a SHOULDER-to-Arms from Hands LEVER action (touch attack) required to add lift, Push Acrobat's HEAD/BODY past obstacle adding push-off momentum providing clearing for acrobats HEAD from obstacle/Foe in the Required Mid-AIR Roll to place feet firm under body & if success Landing facing back-to-back. Then Number of factors that can go wrong BEFORE your feet/body touches the ground? .. ? ..? ;)
... Ugg umm Ceiling height? Pole-Vault Acrobatics, by official vault pole. or use a lever-jump style off a Pole Arm, tho at likely at some extra DC penalty. Mechanical tool assisted Jump of a Somersault = Pole Vaulting and it's DC is much Harder - as effect is more effective height and distance covered.
Depending on the Ground type, smooth/rough, stone/ice-glass, Sloped/Angled, Examples: Mild hindrances add 2-5 extra DC each. Polished church floors/flat DC+2 to 5, Cave Floor with normal tiny rocks/bumps slick(wet/slimy-ish) +2 to 5 upto 10 DC. Semi-Smooth Sloping Up or down tunnels DC+15 to 20 DC Epic level stunt. ON an Angled 40 to 45 degree House Roof/Dry dc+10 or more+ for lose tiles Epic DC level.
Ground surface type (slope & wet/slickness), A Monster's Horns/spikes & tails obstacles might affect DC factors as "a floor surface". It's height &/or body TYPE, length(s) Are VERY KEY non-combat based environmental factors acting the DC too.
Search the D&D second edition 3E 3.5e and a smattering of Modules, Martial Arts ect. & old Dragon published material's like "Pirate's, A Prestige class" give helpful concepts for acrobatics "styles" for possible Acrobatic use actions and Rule assessment suggesting.
-Edited- "the DM sets the DC based on the complexity of the stunt and the danger of the situation." The abstract Key idea: Complexity = is Detail level orientated. 4E Notes: Only player gain from this in combat is for getting FLANKING a trivial -2 status change or to flee.
Shimonyk, What your question is literally asking is not the DC total of this "feat, stunt, maneuver" itself but for an ADD-on DC TO THE BASE DC15 for EXTRA ATTACKERS ( reflex score? multi stunt rolls then for each if hit for success? :P ) & for EACH OA to have differing or added hit problem to the TOTAL STUNT's DC!!. While initially fumbling around with possibles of adding Extra game mechanics to 4e thinned basics. Original D&D upto 3.5e basically said, Any normal Hit DMG during the "Acrobatic maneuver Somersault" = Stunt = Blocks the motion's feet landing = Failed and acrobat Falls prone in hex moved to (and likely option to GM for Fall Damage). If I Remember Correctly the Errata, been a few years.