Nah. You are totally allowed to do that. You’re allowed to micromanage them in two ways:
- Adjust padding using existing panels that allow it. (EDIT: this is most of them)
- Write a custom layout panel.
Writing a custom layout panel takes just a bit of time (especially the first time you do it), but it isn’t particularly hard. And that panel can have pass-through logic that just asks for X,Y,Width,Height and applies them to the widget. We actually have a panel like that (SCanvas) and it isn’t particularly useful in practice. And, as I mentioned, we are adding a better version of that panel in UMG.
BTW, we don’t use Pixels in Slate. Everything is specified in Slate Units (SU). This allows us to run Slate at different pixel-per-slate-unit ratios, which is required for supporting high DPI monitors.