Handlers header improvement (#6802)

* redo the header size

* rewording the header text

Author: soujay

nservicebus/handlers/index.md

@@ -19,7 +19,7 @@ If using the Request-Response or Full Duplex pattern, handlers will probably do
 
 If handling a message in a publish-and-subscribe scenario, see [How to Publish/Subscribe to a Message](/nservicebus/messaging/publish-subscribe/).
 
-### Mapping to name
+## Mapping to name
 
 Incoming messages will be mapped to a type using [Assembly Qualified Name](https://msdn.microsoft.com/en-us/library/system.type.assemblyqualifiedname.aspx). This is the default behavior for sharing assemblies among endpoints. When a message cannot be mapped based on Assembly Qualified Name, the mapping will be attempted using [`FullName`](https://msdn.microsoft.com/en-us/library/system.type.fullname.aspx). The following is an example of how NServiceBus gets the type information.
 
@@ -28,7 +28,7 @@ var fqn = message.GetType().AssemblyQualifiedName;
 var fallback = message.GetType().FullName;
 ```
 
-## Behavior when there is no handler for a message
+## No handler for a message
 
 Receiving a message for which there are no message handlers is considered an error and the received message will be forwarded to the configured error queue.
 
@@ -44,11 +44,11 @@ If it is not possible to design multiple handlers in one of the ways described a
 
 There are a number of techniques for making this change, depending on the type of message:
 
-#### Events
+##### Original message is published as an event
 
 If the original message is [published as an event](/nservicebus/messaging/publish-subscribe/), the handlers must be hosted in separate endpoints. Each endpoint receives its own copy of the original message, isolating the failure of one handler from the others.
 
-#### Other messages
+##### Original message is sent to an endpoint
 
 If the original message is not published as an event, but rather [sent](/nservicebus/messaging/send-a-message.md) to a specific endpoint, the following techniques may be used (listed from simplest to most complex):