The T10 and X6 can be run at the same wattage. smok recommends that the best range for the X6 is 80-100 watts and the T10 80-110 watts so I think it is safe to say 80 watts should work fine for you. These coils just need a good amount of watts to make them come alive. Look at the bright side; at least now you can actually use those higher watts your mod provides but you never used.
Also how old are your batteries? I only ask because as batteries age they can lose some of their oompf. Batteries do get tired.
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Good to know. Just bought 2 sets of batteries but who knows how long they were on shelf in warehouse or vape store. Do they have dates on them to check? I never noticed any.