I'm assuming you have this aimed right at 88 degrees magnetic?
Also is that report accurate in that your antenna is only 10ft AGL?
I would try the HDHomerun directly to see if that solves your problem. If it does then you likely just need to add a drop amplifier such as or similar to:
4-Port drop amplifier.
Use that in place of the passive splitter.
Some tuners are more sensitive than others unfortunately.