Minimum space between insulated riser and barrel for a 6 inch rmh

Off topic perhaps, but my crap phone isn't allowing a new topic....
How much space is minimum between insulated riser and barrel for a 6 inch rmh?  Now I am volunteering labor for this build, and the riser will be a tight fit to slide over
Thanks for any help

The build so far

A storm has slowed our progress, but still wonder if 6- 9cm is enough space between insulated riser and steel barrel. I have read multiple threads, as has Paulo, we only find specs like 5 to 6.8 cm between riser and top of the barrel
Thanks, folks

Hi Rico, perfectly acceptable to offset a barrel, leaving an inch or so to the barrel on the one side.
The other side would have 6" or more.
If you make the gap too small, you will have issues; it may stall, and smoke back, your buddy's wife might not be happy...
Perhaps 9cm ( 3.5") would work, but 6cm may not.
The CSA must remain the same in the J-Tube, and the barrel CSA should be at least 150% larger.
Page 9 in the RMH builders' guide shares that information.