More doc for Gridset compatibility check (#9261)

docs/user-guide/layer-settings.md

@@ -102,7 +102,7 @@ When the *Use cache options* is enabled, more controls are enabled so that it is
     <img src="../img/layer-settings/warning_info.jpg" class="ms-docimage"  style="max-width:300px;"/>
 
 !!!warning
-    The Gridset compatibility check made by MapStore whose result is shown by the Info tooltip, is usually quite reliable but should be considered anyway only to provide general matching indicators aimed at highlighting possible compatibility issues between the current layer/map settings and the remote Tile Grid. Due to the cache tolerance considered on the server side by GWC, it might even happen in some cases that the settings available on the client side don't HIT the tile cache even if all the checks listed are successful.
+    The Gridset compatibility check made by MapStore whose result is shown by the Info tooltip, is usually quite reliable but should be considered anyway only to provide general matching indicators aimed at highlighting possible compatibility issues between the current layer/map settings and the remote Tile Grid. Due to the cache tolerance considered on the server side by GWC, it might even happen in some cases that the settings available on the client side don't HIT the tile cache even if all the checks listed are successful. At the same time, when the standard gridset is used, gridsets check may fail even if all WMS request are effectively HITTING the cache (e.g. because the WMTS reports a list of origins).
 
 * Set the layer *Legend* with custom *Width* and *Height* options. Both of these field values if greater than the default legend's size of 12, then the custom values gets applied on the legend width and height display property