I've been thinking about this based on various things I've read recently and trying to work out the reason. I don't really know the answer but here are some thoughts...
Temperature play a big part in this. As you say James, staying too wet in the middle causes problems, and I think you (possibly someone else) have said in a different thread in the last few months, that it's cold and damp that really does the damage.
But in cooler climates it's hard to avoid that with either moss or bark unless you are willing to heat the house just for the orchids. I don't and I have a lot of orchids, I don't know, but I would guess beginners don't either. So... in everything except the summer (and even some of the summers we get here) the temps in my house range from 60-70, at this time of year we are mostly around the 65 mark, similar in spring, in winter it can drop down to 60 when the heating is off (all night and a lot of the day as well) will be about 67 morning and evening, and will only go up to 70 if we are feeling chilly and have decided to have a little more heat.
So... (talking about Phals here, I actually grow cool loving in orchids in moss anyway)
a. Phal roots in moss struggle because the cool climate leads to slow drying but also the cool climate combined with always damp is a problem.
b. Phals established in bark need the watering dropped, sometimes as low as every 10-14 days (although I know they really struggle if they don't dry in that time and I prefer closer to 7 days). The cool weather means it takes that long for them to dry (even in really large bark). In the summer warm weather I can water even if it's not fully dry, but if I water before they are fully dry in the cooler weather the roots start to show signs of stress. I've lost orchids this way in the past, a heat mat saved others but I can't practically put all my phals on heat mats.
c. Phals established in moss need more moisture around their roots. In the summer/warm weather I am guessing they can be put in medium/large bark, with good air flow and watered very frequently. However when I've tried it (not in the summer) the roots have quickly died, whether I've watered frequently or tried watering when the bark is dry as I would with those established in bark (7-14 days depending on pot size and number of roots).
d. Phals in S/H do well in the summer, but roots show stress in the winter and again I've lost an orchid that way, and saved others with a heat mat.
Why do they die in case c & d. I don't know for sure, but I am starting to suspect it's temperature, combined with the roots tailored to need a more moist environment.
For phals bought in moss, for me keeping them in moss doesn't work for me either, I've tried that as well, and I've tried transferring them to S/H, but see case d.
Those I buy in bark I have no problems with. I've bought around 30 in bark over the years and 25 are still with me, and all of them did well for at least a year. I've bought around 10 phals in moss, and only been able to save 2. The last two I ever got bought in moss.
For me Leca, but not S/H, is the solution for these ones bought in moss. When dry it is warmer than bark or moss, when wet it can get colder due to evaporation. This colder due to evaporation is the reason S/H doesn't work in my climate for phals (I use it for other cooler growing types, just as I use moss for other cooler growing types). However growing in it as a straight medium it dries pretty quickly and it has lots of air flow.
Now... I've not thought about it until today, but is the fact that Leca tends to be warmer than bark or moss when it's dry a big factor in this. My phals in it are probably watered every 3 days, and will usually be dry for a day at least. Is the temperature a factor?
As I said at the top of this long post, I don't know the answers, only what I've observed. James we are in very different climates, Phals as warm loving orchids probably have an easier life in your climate, I'm probably growing them at the lower end of their 'happy' temperature zone. I wonder, just wonder if that is the reason for our different experiences of this
But, obviously, even if you can't keep them warm, it's just a matter of finding what works. I've seen your Phals Rosie, and they are beautiful, so I know that what you do works! 
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