P131, Playing a Game of Bolt Action, Scenario Special Rules, Setting up Observers and Snipers, first para, first sentence establishes that the set up rules are the default ‘Unless players wish to agree otherwise…’.
Same heading, third para, first sentence states that units in reserve can’t use their special set up, then goes on to say those deployed on table and in first wave can use their special set up. Applying both those, the only scenario which prevents forward deployment is one in which your side starts with all your forces in reserve, no on table deployment and no first wave, or where you’ve agreed not to use it.
The only scenario in the MRB that meets that requirement for either side is ‘Top Secret’, p138. Set up is “No units are set up on the table at the start of the game. All units on both sides are left in reserve (see p132).”
All other scenarios, both sides have either units on the table or allocated to first wave – if you choose to leave your snipers, observers, or units with spotters in reserve it’s your tactical decision stopping you, not the scenario.
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