Duplication size too much

Hi;

we are doing full backup every night and then morning we started  we sent duplicate some other storage device over wan but the full backup size 3-4 gb on the other hand the duplicate job takes 100-200 gb so we have to cancel job for release bandwith over wan. why? the differences so much also we selected option most recent full backup. Or any way to limit bandwith usage to sent over wan?

Thank you