I have the same 27 HFS and am also looking to upgrade to the Tri-Glide. As already mentioned, there will only be 3 inches or less of front to back slop...that's 1.5" on each side. I'm thinking there are two options. First is to offset the trike lightly and let the front wheel go past the bathroom door. You'll have to secure the bathroom door somehow to keep it from banging/scratching the front of the bike. Second and better option, I think, is to pull the trike in (centered) and at the very last, crank the front wheel left or right. That should give you a few extra inches and yet not pull the bike off center too much. Being a trike, the front wheel does not need to be straight in order to keep it stable in transit. Just my thoughts.
Honestly, I'm more concerned about the ramp door's ability to handle the heavier bike, especially if you need to raise the bottom edge of the ramp to lessen the angle between the ramp and garage floor. I have to do that to keep my current Ultra Classic from bottoming out over the threshold. I'm already on my second ramp door, thanks to Lippert's poor engineering and manufacturing. They have over-promised and under-delivered on these ramp doors.
2015 XLR Hyper Lite 27 HFS
2008 Harley Ultra