Canvas becomes too big when generating tabs on a content canvas

Question

I want to generate the following layout:
<New content canvas> block 1 height 15 width 80
prompt: field
prompt: field
<New tab canvas page> tab 1 height 31 width 80
Multirecord block which is a detail of block 1
<New tab canvas page> tab 2 height 31 width 80
Also MR block which is a detail of block 1
Window height 46 width 81
Problem is that the height of the tab canvas pages becomes 46 and not 31, so the height of the window becomes 61. I've tried several options, als with view height and width, but it is always reproducable and wrong. And with every module I build with the same sort of layout.

Answer 1

When i'm not been able to get the right size i will add a pre-form-trigger and resize the object at runtime. It's saves me a lot of time instead of trying to instruct the generator to do so.
I'm always using the pre-form-trigger and not the when-new-form-instance-trigger because Headstart will do the initialization after the pre-form-trigger is fired and so it's taking the changes made in the pre-form-trigger into account.