Quick question. But if the coil fits can you vape it? Like say I somehow fit a Clapton dual Into a kanger subtank... Can I just vape at 60 watts? What's the difference isn't the tank just holding the coil?
If you mean just pop in a factory coil head from a different manufacturer, as a rule... no.
At a minimum... the height must match for a proper seal.
For example Aspire coil heads are one of the couple/few than many brands design their tank to accept, as well as their own brand... but those are the exception.
SMOK TFV4 head in a Kanger Sub Tank... I haven't tried, don't have a TFV4.
Why don't
you tell
us ?
If you mean... "How big a build can I stuff in my Kanger RBA deck?"... that's a different matter.
Just getting it in without shorting to the coil chamber housing isn't enough.
These things are actually
designed and
tested for optimal performance.
Smart Johnnies and their maths... that sort of thing.

Extra coil mass will be blocking airflow through the chamber... gonna be a
hot time.
But there's no telling where the break even line is without someone trying.
If
that's what you want to experiment with... go for it.
For safety's sake though... use a regulated mod, not a mech.
Things can go very bad, very fast with a hard short.