I mounted my XS650 breather there...Looking at the PCV reed breather supplied by Holland Norton Works. it appears to be mounted to the top frame tube behind the air filter ... To get the best operation from this valve shouldn't it be mounted as close the crankcase as possible...
I take it you have the crankcase mounted breather? ... so did you use a short section of hose between PCV & OE breather body.I agree the best vacuum signal is at the source. So on my '73 750, an XS650 reed valve is mounted directly to the crankcases where the original breather elbow was. I had to trim the waist of the reed valve body on both sides and fabricate a clamping plate, to hold it tight to the cases, but I was able to use the narrower pattern of the breather's bolt holes. Not pretty but effective.
Looking into the oil tank at the breather return, that reed valve starts returning wet sumped oil with a few key off kicks. Between the reed valve and the scavange side, I don't get all of the sump's oil, but it helps.
I note with some curiosity that it's shown mounted horizontally (scroll or search the linked page for 'PCV engine breather valve #H14') with both spigots at the same level – I don't see how condensate can drain like that so I wouldn't do it, but Constant's the expert here and might chime in …? Maybe it just pools there when the engine's shut off, and it doesn't matter.