The plants look still very short. I would like to ...

Hello ! Hid 400w is good at 40cm (from the top of the plants) without cooltube and 20 cm with coultube so 30cm or 20cm could be good in your case. If you just want to make your plants stretch then put the light higher like you said 60cm could be good but they will only get taller without real beneficts as the space between the nodes will be hudge and you could loose light penetration to the lower buds. I hope it will help you 😁👍