The 10m lines were actually on a 45cm bar. Worked fine.
While normally I would use a 55cm bar on the 12m HL.
14m has been my most used line lengths the past year, on all kites from 5m up to 19m R1.
Now using more different lengths on different kites or in different conditions. Currently got bars with 10m, 12m, 14m and 18m lines.
Back to your question: It wasn't actually the lowend of the 12, as described, so no loops were needed to get going.
If a loop would be needed, no it would not be suitable! Apart from lack of generated power it is also a problem of available space to loop the kite while not riding.
In that case I would go for 14m or better 18m lines really.
By no means using 10m is what I suggest here, it is just a report from my experimentations. If you would like to do the same, go for it, but you need to find out what works for you and what doesn't.
Line length is a very personal thing really (especially when it come to going quite short of course).