So yesterday I dropped 2 x rare laquered plates, and today I just got mavina's diadem.

It got me wondering, does this mean that I was very close to getting 2x tals armor and a griffs? Is that how it works?

depends on where it dropped

wsk and chaos

then yes

my mf is 365....hypothetically in this instance would higher MF have helped?

Technically, yes. But if you kill any slower with more mf% it may offset anyway

Let's throw in some numbers that i found on the german drop calculator.
With 365% mf you have:
+148% to find a unique
+210% to find a set item
+226% to find a rare item

Let's say you get +100% mf. The numbers are now:
+162% unique
+240% set
+261% rare

Not a huge boost to your chance of finding a unique item. ( about 5,6% higher chance than with 365mf ).
You'll notice that the chance of getting a set/rare item get a good boost.
However, this does NOT mean, that your overall chance of getting a unique item gets lower. Upon dropping the item, the game first decides if it is a unique item - if it's not, it will have a chance to be a set item. If it's not either, it can be rolled rare, and if that is not the case as well, it will be magic (or could even be white/grey, depending on the item)

gotcha, seems real marginal