some add ons
- you dont have the possibility to join defending arena through a raid; only solo marches can be sent. so indeed march boost are vital here (so was 640 % , even more now the newest 3250% )
- the total capacity is now up to 310m troops ; except some top roders it is unlikely you lose anything if you smarlty fill in. with all due respect, a 1T order or less, with still many people under palace 35 or not having ann yet : dont send 30 marches without hero, those will die
- also, (but again it depends on the overall status of an order, hard to give a one size fits all advise) worth remembering that if you practice the 'last secund defense' (= not filling in the arena, but coordinating sending your troops 1-2 sec before the NPC arrives) you can choose which one you defend. in other words being an arena L4 does not oblige you to defend all types of NPC. even in big orders it is often seen that at some point the last one to run it, stops, as it got enough points from attacking the order which ran the Anrena first and by doing (ex) 15/20 marches of their own (they stop to avoid being hit and giving back their score advantage).
- finally, it is also a non sense to not go for the arena or most of it if your opoonent does not have a citadel L4 ; excep tthe rare case where you would face 4 giants jumping for other reasons and landing in an non -maxed citadel order that would destroy you, it is unlikely an order with citadel L3 has the capacity to fight. All goes along so if they aren't L4 arena, they are most likely also behind in many fighting areas.
Besides , up to the last update of the game, trophies are the 'most wanted' item if you play the game as fighter so instead of sparing yourself with a safe win, grab each opportunity to gain trophies. Trophies will bring you more on a long term basis than the tower of triumph from OVO win or the satisfaction of clean ovo win stats :)