To limit players from holding back on the XP just for the purpose of SWB rewards - I suggest that XP should be harder to avoid.
It is pretty lame that players stay in the lower field griefing new or cacual players just for this purpose.

Suggestion is to add XP reward for :

Survival Trial

Plunders and Convoy

Also, automatically claim 25% of the XP every week from daily/weekly missions not compleeted.