Lets say there is a chart with pisces ascendant and 1st cusp is at 10 degree pisces and mars is in 5 degree aries, and aries has 2nd cusp in 6 degrees.
My question is, Mars is in 1st bhava or Mars is in 2nd bhava, since the cusp started from pisces ends only after the Mars 5th degree i.e 6 degrees?
In Rasi chart:
What I have understood from Ernst is that grahas are placed in rasis, not bhavas. So Mars is in Aries.
With respect to Bhava cusps, we consider them as points (like Ascendant degree is cusp of first house, similarly other cusps are also points). So in this case we can say that Mars is conjunct 2nd Bhava cusp (rather than saying it's in 1st or 2nd bhava)
If you are looking at Bhava chalita chart, then things may change depending on what chalita system one is using.
Regards