There's no "nearly fully load" order option and you know it
If I had those trains set to fully load (doesn't matter wether it would be any full load or just fully load) that station would get jammed pretty soon, because rafinery has fixed 6/8 ratio. To compensate for this and any loss caused by ratings I could deliver some oil from nearby wells or rig but that is not possible in every game and that's why I began to look for other solutions, more universal, not dependant on convinient industries' locations.
Let me get back to my setups being too too complex. I'll briefly describe how I do it and what are - in my opinion - advantages of my 2 way oil lines.
I only have to issue all those orders for a single train - I usualy do it for the first train before it reaches rafinery and yields 1st income. It's all set right from the start - with one exception - load threshold is set to 1% (why, I'll explain soon) and I just don't triger PT / CH at Rafinery station, therefore in beggining trains always jump back to oil wells. When I feel ready I send a truck to begin production in rafinery. At this point oil wells still pump basic output, that's why it doesn't matter how loaded trains are because there are only several of them. I set threshold to 70% after I can maintain constant suppies for oil wells. Setting up orders for trains to service another source of oil is done with 3 clicks - clone a train from main line, feeder load (replace first order), add refit to oil to that order - and that's it.
Having 2 way oil trains has 2 main advantages - 1: it reduces traffic on oil / PT / CH line by about 1/3 and 2: having all chemicals transfered to single location near claimed town opens numerous play scenarios, because you can do so much with it!
Are quarries scarce in your area? Well, get some sand transfered and distribute it with a truck once per month to glass works and flood it with all those chemicals - you get decent BM production to start growing and some manufacturing supplies that you can use to make food. If you want to forge some metal, well, chemicals will help at aluminium plant, then in metal workshop and metal fabrication plant. Is metal branch too complex? Well, take those chemicals to a paper mill instead, then you only need to stuff it with wood and clay to get all the goods you need and same amount of MS that can be magicaly transformed to alcohol at 8/8 ratio with a single truckload of fruit or grain. I consider chemicals the most useful resource - right next to the great trinity: ES, FS and MS.
edit:
ah, forgot to clarify - low ratings are not shifted to 2ndary station, that station has high ratings because of little train visiting it fequently, lower ratings are kept on main station because there is cargo sitting there, dropped by trains that didn't reach the load threshold. And high ratings on 2ndary station have no affect on main station.
Take a look at this
chart
, maybe it will help you understand when rating is being actualy pushed because - as I said before - rating pushing cheats only work up to certain point and there are way too many factors involved to close it within single definition.