its funny but evean I dont know pure and 100% correct answear to this

maybe reason is that necro almost never dies which ever path you take...
if its PvP full block.
if its PvM with gear i would probably go Full block this time (evean I argue lots of times against full block)
If its like me PvM with maxed MF possible,
its full vita... you know its quite hard to get max block with monarch 4xisted (unless you are lucky and got Jmod - worth around 400high runes)
but maybe with this 4isted monarch i would still have around 40-50 chance to block which is also good..
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I think when i go summoner hardcore, I'll go full block this time... so thats my advice
here is why...
dex needed
most people get at max to level 94
so its 210dex that you need at level 94 ot have full block with homo.
if you count some stuff off...
210 - (20torch+20 anni+15waterwalks+2shako+5mara+25base starting dex)
left 123 dex to put in dex
thats 246 life, with BO at level lets say 16 thats 80% its 246*1.8=442
if you get COA or have nice resists you can socket homonuclus with eld that increase chance to block resulting in only 106 points in dex... (here maybe would be better to count if ber or jah wount be better over life saved by not go dex)
not to mention u can get pair of some awsome rings and amulet...
this is where funny decieding starts...
THrou my gameplay as necro full vita, I died only from elemental attack... in the beggining of building necro with not maxed resists..
later with whole gear on i didnt die yet...
as it seems to me 75% of resists take care of all elemental attack (not to mention i got only lighting at 70 now that i MF)
so thats left us to deal with physical attack.
in here most of people would thought that full block is good
so do I, but i was thinking...
what happend to me some times, is that i am left in one seckond with 80 life, in same second i drink full reju potion.
So your life is not really only life that you got in bulb, but what you can get if you got time to react..
barbarians dont die just becouse they got 5000life but becouse when they see low life they drink full reju. And when they see low life, they still got 1K of it... hope you get what i mean
I didnt think i wrote all of this

hope its helps...
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As i sad i dont know for 100% which is better
but ill try full block when I go next necromancer. As I see it Necro wount die cosue of one or other but becouse of some bad decision in gameplay...
AnimeCraze is totaly right...