Harbeth Super HL 5 Plus room size?

No issues in your room especially if you listen as close as you described.   They can create some bass modes near the wall behind the listening spot in smaller rooms if you are backed up against it.  

I had them in a smaller room for years with no issues whatsoever.  They are made to be used in small rooms.  Go for it!

I have Harbeth SHL 5+ 40th anniversary in 18x12x8 room. 36inches from rear wall. 8 feet apart. My chair is about 9 feet from the front speaker plane. Sounds great. I also have a pair of the P3esr 40th that I one afternoon put in the system using the same footprint. Amazing how good they sounded; not the full sound of the SHL 5, but good nonetheless. If you can I recommend the 5s.

You should be fine.  Harbeths actually seem to do pretty well in "normal size rooms," especially as they probably originally targetted British homes (I believe Alan Shaw has said so).

In any case, my Harbeth SuperHL5plus worked fine in my 13' x 15' room, in terms of even frequency balance, no bloat etc.

My only issue was a somewhat limited soundstage depth.  Quite a number of other speakers produced more believable depth and dimensionality in my room (including my current Thiel speakers).

The Harbeth speakers didn't seem to have this noticeable problem in the stores, but then the store auditions I had were in a large demo room.  So either they bloom in soundstage in a larger room, or perhaps it was because I was sitting further from them at the store and so due to that the soundstage seemed deeper.
FWIW....