I find mixing media doesn't do anything for me but cause confusion and up the likelihood that I will overwater (because I am physically unable to underwater a plant apparently). I know how solid sphag and solid bark perform, I prefer just to adjust the size of the bark chips if I need a more retentive medium. Combining seems to make both of them break down faster than when they are solo.
for what it's worth I use a percentage of sphagnum in my paph and phrag mix. coconut based with lots of sponge rock. but I like the 10% sphag for moisture retention and initial antiseptic properties.