I think this depends of the writer and even the story.
I think the best example of how the rings are ¨suppose to work¨ is with
Mirri Riam
and maybe this might be just my interpretation but it think it works logically
she loved her husband, she had this great emotion inside her heart, then her husband died and that leaves her... not empty of emotion but more like without focus as the object of her love is not alive anymore, thats why the ring choose her, because she has ¨has great love inside her heart¨ she fuels the ring and not the other way around, just like all the other rings.
and of course it works with other kinds of love but I think that the main idea is the capacity of having an strong emotion with another
being.
remember a lot of the powers on GLC and even the tv show came from connecting people, so loving the corps very very much is just pretty stupid reasoning for steward to use the ring.
on the case of fatality and other sapphires who were converted I guess that the idea is that the crystals put them on an illusion state that shift their own emotions to give the priority to love, she hated John Steward because of Xanshi and used that hate to instill fear, so then the crystal shifts that emotion around because it is still an strong sentiment with Steward, it is not like it forces her to love him but changes her on perspective so she takes the decision to love him and when it comes to that realization is when the ring can now use that emotion to fuel itself.
It is not just because steward was the closest person to him at the moment, remember when she was converted from a sinestro corp her first order to the ring was ¨find john steward¨.
now, i didnt read the issues of GLC so maybe i might be mistaken on how it happen but as far as I understand the story is that the ring was the only reason why she loved him or something and the ring gets destroyed so now she hates him again. which is retarded because it would mean that she was just an slave to the ring the entire time and means the same for pretty much all the other ss on top of it being
highly contradictory the way that the thing works, it is not like the indigo that actually forced the emotion on them.
the ¨fulled with fake love¨ thing just makes no sense with this just like it wouldnt make sense with any of the other rings.
and I think thats also why it is such a huge gigantic pile of bull**** when it came to Carol, if fatality´s explanation was bad with Carol is far worse because she leaves Hal under the stupid pretense that she needs to be in love to fuel the ring or cannot be with Hal because Venditti is just a very poor writer and for some goddamn reason editorial wanted to ship her with Kyle.
overall I think this is just an example of bad direction that came simply from the writers not understanding how the concept worked from what Johns did.