I have been trying to tension the chain on my girly. There seems to be a plethora of ways to do it from the Haynes manual and Service manual method to many methods used by others, some contradictory and none fully satisfactory to my mind. I think i have lit on a method that really works. Put the bike on the sidestand to help with compressing the suspension then put a small ratchet strap from the front pannier mount and round the back of the swinging arm, one on each side. Tighten them up to the limit of the suspension then adjust the chain tension so there is still a little slack. If you don't have the triumph pannier racks I'm sure there will be somewhere else to put the strap. When you have taken the straps off put the bike on the centre stand and measure the slack at the centre of the run, that is your chain tension in the future.
Or.........with bike on side stand, gear selector in neutral,
Set chain with about an 1 inch to 1 1/4 inch slack .
Done.
The problem I have with a fixed measurement on the side stand is that it will vary with the weight on the carrier rack and with the amount of pre-load set by the owner. By setting it so there is still a little bit of slack at full suspension compression it is then impossible to have the chain too tight.