@andyg I moved onto Lantus / Novorapid about 8-10 years ago. Could be longer, I really don’t remember 
Back then I was on something like 26U of Lantus at tea time and that worked perfectly for me for about 5 years.
After that it just packed it working and my sugars started soaring in the afternoons. I was getting home from work to a BG of 25+
A week of intensive blood sugars later and it looked like the Lantus was just flat running out after 18 hours or so, dose-age was irrelevant as increasing it didn’t help at all. I started hypoing all over the place.
Increasing my Novorapid wasn’t really an option at lunch time as I was already taking 20U+ (depending on the meal of course) and I was advised not to push it over 25 as it wouldn’t really have much more effect.
Had a lengthy conversation with my diabetes nurse at the time and she suggested I try splitting the dose and taking it mid morning and before bed. The principal being to spread it out over the day.
With the exception of the recent issue making me lower the evening dose, this system has worked well for me since then.