Self answer, for those who could be interested 
The index.html page stays the same
In the main.html template file, I changed the
<ion-nav-view>into<div ui-view>, and put it inside a<ion-content>tag :<ion-content>
<div ui-view name="main-view"></div>
</ion-content>Then in the main-view html templates, I just directly write the content I want (here a padding div, for example) :
<div class="padding">
...
</div>
Hope it can help somebody.
Arnaud