I've not been suggesting changing the dose - the dose has been suggested by the doctor : "my doctor said i should use the same dose". We're just discussing what you need to do to achieve that - and the answer is to do what the doctor and the toujeo leaflet says, and ignore the concentration, just think about the number of units.
That dose will be in U, not ml, as all insulin dosed in pens is these days.
Re "about a third stronger" - actually, no, it's 3x the strength, 300u/ml vs conventional 100u/ml. But if you try and think about that, that's where things go wrong. The pen takes care of the different strength for you, and if you try and think about the volumes, life can get confusing and dangerous.
So no, my advice is not incorrect. I do know what I'm talking about - I've got the pens in the fridge, I've been through this, and I also don't have any trouble with the concepts involved. To repeat it : Stick with the U numbers, don't think about the concentration, use the pen it comes in rather than anything else, and it'll be fine then.
Now as for tweaking the dose a little higher as per the leaflet to cope with the higher BGs - I've not engaged in that discussion. Personally I had to take a little more Toujeo than Lantus (as in 1 or 2 U in 17 or so) - and I worked that out myself, because I don't see the doctors frequently enough to change things as fast as they need to. But that's got nothing to do with the concentration and dosing, it's about the slightly different effect it has on the body.