Hi @jan, You do have the right idea. However, the In Heights column only really works when you use the Russian standard tables where the length and width is minutely adjusted according to the height and width of a person, so I advocate to ignore the height column.
You may create a multisize file for each set of sizes that use the same increment values. This would normally be only 3 files: Size 34 to 44 with 4cm, then Size 46 with 5cm and then Size 48 to 52 with 6cm.
When it comes to height, most patterns will tell you how to adjust the pattern for height, however, Seamly2D doesn’t do this, so you could use formulas in your Variables table which you use while creating your pattern.
In this topic, I also discussed this a bit: Différent increments for multisizes
Have fun 