What determines whether a portal will drop a key as a result of an xmp blast

As we found out today loot item quality depends on the following things:

• Portal level - the higher the better
• Level of the strongest resonator (I believe it determines the maximum item level you can get from the portal, not confirmed)
• Player level. We made an experiment today L1 and L6 players hacked the same L4.75 portal several times today:
  • L1 player's loot consisted of L1 and L2 resonators and XMP + common shields
  • L6 player's loot mostly consisted of L4 items + several L5 and L6 items + rare and very rare shields.

It looks like in the portal hacking phase, the level used is the "rounded" level.

• the XM cost is based on the portal level
• the attack you can receive in response of hacking an enemy portal is based on the portal level

It sounds logical that items dropping is related to this "rounded" level.

As far as I experienced it (i'm now level 7), to get high level items, I have to hack "real" high level portals.

A portal at level 5.75 ( 7+6+6+6+6+5+5+5, made by 1 L7 and 1 L6 player) will still give me less high level items than a real L6 portal ( 7+6+6+6+6+6+6+5 made by 1 L7 and 2 L6 players).

I never get any L8 items from portals that were at lavels 5 or 5.25 or 5.75, the first time I got some was when hacking a real L6 portal :D