How do you currently limit access to blocks? The preferred way is to have your train lengths configured along with the block length - this will determine if a train can stop in a block.
However you can also do it by using permissions on the route if you are running fixed trains thay won't change so you know what can fit where.

So if I understand correctly you've setup your staging yard with two blocks in sequence, the second one longer than the first. So you'd just create a route from the approach block to the second block and add the first (shorter) block as a crossing block.
That way if the longer train can't fit in the shorter first block, it will use the route to the longer second block assuming the first (crossing) block is empty.

Hi all,

Apologies for not replying sooner.

I found a solution, which was to create the via block route. I since read your comments as well, which has helped also.

Thank you so much!

Eddie