There are several factors which may impose Casting Constraints. The Casting [method] for manifesting capabilities relies on specific conditions. The ability to cast without ANY impediments (in an unfettered state) is referred to as Unfettered Casting, and gains a caster an extra measure of Concentration.
Spells have no Initiative[/su_permalink] adjustment.
Initiative penalty = Spell Level (min 1); Spell Save DC / Attack Bonus: -1; if done On The Run[/su_permalink], a Steady Focus[/su_permalink] check must be made to execute it (failure = Disadvantage on attack or Advantage on save for target)
Militant Casting: War Wizard feat, Eldritch Knight
DC 15 +spell level [mystic-practice] or spell failure; if done On The Run[/su_permalink], a Steady Focus[/su_permalink] check is required (success = Disadvantage on attack or Advantage on save for target / failure = power manifestation fails); initiative[/su_permalink] is halved
Adjurations are fueled by the bond between a Divine Principal and the caster. These castings are not hampered in any way if the caster has the correct familiarity and/or proficiency with the armor they are using.
Spells are Occult manifestations are require the most freedom from constraint.
Invocations, like Adjurations, rely on external forces of the Pact. These castings are not hampered in any way no matter what armor they are using.