Like jdangler I have a 4wt scandi short versitip
line for my 4116 sage one - the version of that head designed to use light tips. The tips it comes with are equivalent to 4wt rio
replacement tips and weigh slightly less than 50 gr at 10’. I’m not even sure you can buy those separately - I’ve only ever seen 5wt ones for sale - but they are labeled as such and I have weighed them. My understanding is that the versitip version of the scandi short is equivalent to your line with the tip cut back, so think of your line as the versatip with an integrated floating tip. Unless you already have the versitip version - doesn’t sound like it. So with that as a reality check you definitely don’t want to be using a heavy leader with it, not even < 50 gr light tips like the ones that come with the versitip version of that line. Just stick with a tapered mono leader, approximately rod length, and consider switching to the versitip version of that line if you want the added functionality of using tips.
Either setup - scandi short versitip with provided sinktips and a few feet of tippet, or scandi short with a tapered mono leader, should work. So as suggested above put some more time in with it and see how it goes.
As far as the leaches, it depends on the fly but if it has some (waterlogged) rabbit in there that might be iffy with that line too. Perhaps try something very light first to remove that variable. As mentioned above the skagit is your friend in a pinch - that is a really light setup you are using after all.
Edit: For what it is worth, the Nextcast WA35 330gr (uses tips as well) is awesomely easy to cast on that sage with more beefy flies. It’s feels more like a scandi head - less clunky than a skagit head, but with much of the power.