Shield Defense... Which Alpha?

Hey folks, am looking for some advise on which alpha to slot for my BS/Shield Scrapper.

I've so far slotted for Defense almost exclusively but given my options for the alpha I am thinking Cardiac Radial will help improve my Squishiness when I DO get hit.

Here's my Build:

Hero Plan by Mids' Hero Designer 1.90
http://www.cohplanner.com/

Click this DataLink to open the build!

Level 50 Technology Scrapper
Primary Power Set: Broad Sword
Secondary Power Set: Shield Defense
Power Pool: Flight
Power Pool: Medicine
Power Pool: Speed
Ancillary Pool: Body Mastery

Hero Profile:
Level 1: Hack -- Mako-Acc/Dmg(A), Mako-Dmg/EndRdx(3), Mako-Dmg/Rchg(7), Mako-Acc/EndRdx/Rchg(11), Mako-Acc/Dmg/EndRdx/Rchg(19), Mako-Dam%(40)
Level 1: Deflection -- RedFtn-Def/EndRdx(A), RedFtn-Def/Rchg(5), RedFtn-EndRdx/Rchg(7), RedFtn-Def/EndRdx/Rchg(17), RedFtn-Def(27), RedFtn-EndRdx(39)
Level 2: Slash -- Mako-Acc/Dmg(A), Mako-Dmg/EndRdx(3), Mako-Dmg/Rchg(5), Mako-Acc/EndRdx/Rchg(11), Mako-Acc/Dmg/EndRdx/Rchg(19), Mako-Dam%(43)
Level 4: Battle Agility -- RedFtn-Def/EndRdx(A), RedFtn-Def/Rchg(13), RedFtn-EndRdx/Rchg(15), RedFtn-Def/EndRdx/Rchg(17), RedFtn-Def(31), RedFtn-EndRdx(40)
Level 6: Build Up -- RechRdx-I(A)
Level 8: Parry -- C'ngImp-Acc/Dmg(A), C'ngImp-Acc/Dmg/Rchg(9), LkGmblr-Def/Rchg(9), LkGmblr-Def/EndRdx(37), LkGmblr-Def(40), C'ngImp-Acc/Dmg/EndRdx(48)
Level 10: Active Defense -- RechRdx-I(A), RechRdx-I(13), RechRdx-I(15)
Level 12: Hover -- RedFtn-Def/EndRdx(A), LkGmblr-Def/EndRdx(50)
Level 14: Aid Other -- Heal-I(A)
Level 16: Against All Odds -- EndRdx-I(A)
Level 18: Fly -- Flight-I(A)
Level 20: Aid Self -- Dct'dW-Heal/EndRdx(A), Dct'dW-Rchg(21), Dct'dW-Heal/Rchg(31), Dct'dW-Heal/EndRdx/Rchg(33), Dct'dW-Heal(50)
Level 22: Whirling Sword -- M'Strk-Acc/Dmg(A), M'Strk-Dmg/EndRdx(23), M'Strk-Dmg/Rchg(23), M'Strk-Acc/EndRdx(27), M'Strk-Acc/Dmg/EndRdx(34), M'Strk-Dmg/EndRdx/Rchg(42)
Level 24: True Grit -- S'fstPrt-ResDam/Def+(A), Aegis-ResDam/EndRdx(25), Aegis-ResDam(39), Heal-I(43), Heal-I(46)
Level 26: Phalanx Fighting -- DefBuff-I(A)
Level 28: Disembowel -- Mako-Acc/Dmg(A), Mako-Dmg/EndRdx(29), Mako-Dmg/Rchg(29), Mako-Acc/EndRdx/Rchg(31), Mako-Acc/Dmg/EndRdx/Rchg(34), Mako-Dam%(42)
Level 30: Hasten -- RechRdx-I(A), RechRdx-I(46)
Level 32: Head Splitter -- M'Strk-Acc/Dmg(A), M'Strk-Dmg/EndRdx(33), M'Strk-Dmg/Rchg(33), M'Strk-Acc/EndRdx(34), M'Strk-Acc/Dmg/EndRdx(37), M'Strk-Dmg/EndRdx/Rchg(42)
Level 35: Shield Charge -- Oblit-Dmg(A), Oblit-Acc/Rchg(36), Oblit-Dmg/Rchg(36), Oblit-Acc/Dmg/Rchg(36), Oblit-Acc/Dmg/EndRdx/Rchg(37), Oblit-%Dam(43)
Level 38: One with the Shield -- Aegis-ResDam/Rchg(A), Aegis-ResDam(39), TtmC'tng-ResDam/Rchg(48)
Level 41: Conserve Power -- RechRdx-I(A)
Level 44: Physical Perfection -- Numna-Heal/EndRdx(A), Numna-EndRdx/Rchg(45), Numna-Heal/Rchg(45), Numna-Heal/EndRdx/Rchg(45), Numna-Heal(46), Numna-Regen/Rcvry+(50)
Level 47: Grant Cover -- LkGmblr-Def(A), LkGmblr-Def/Rchg(48)
Level 49: Energy Torrent -- Det'tn-Acc/Dmg/EndRdx(A)
------------
Level 1: Brawl -- Empty(A)
Level 1: Sprint -- Empty(A)
Level 2: Rest -- Empty(A)
Level 1: Critical Hit
Level 4: Ninja Run
Level 2: Swift -- Empty(A)
Level 2: Hurdle -- Empty(A)
Level 2: Health -- Heal-I(A)
Level 2: Stamina -- P'Shift-End%(A), P'Shift-EndMod(21), EndMod-I(25)

I'm already soft capped to all Positionals excepting AoE and melee (though melee is more than capped with one application of Parry) and recharge doesn't feel like it would make much more a difference in my playstyle as I am playing now. The other alternative is more damage but it doesn't seem like I'd get quite as much return for my buck as I would from the extra resistances that I have not slotted for at all yet.

Am I missing something obvious here or is going Cardiac Radial a solid option?

Thanks in advance.